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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Appendix D: Intersection Influence Area

On interrupted-flow facilities such as urban street networks and non-freeway rural facilities, the need for the major street through movement to slow down or stop at signalized, roundabout, or AWSC intersections impacts traffic operations along the connecting highway segments. In practice, intersections are represented as point locations in a link-node network configuration; however, its operational effects extend for some distance on the connecting upstream (entry) and downstream (exit) approaches, thus affecting the operational performance of highway segments in the proximity of intersections. Specifically, vehicles may need to stop or slow down as they approach the intersection and then accelerate to the downstream segment running speed as they exit the intersection. Understanding the spatial extent of intersection impacts on connecting approaches is important for an accurate evaluation of operational performance along facilities consisting of multiple segments and junctions. For facility-level analysis, the quality-of-service assessment should not only include the physical intersection area, but also the lengths along all approaches that are affected by the intersection, commonly known as the “influence area” or “effective length.”.

This section summarizes the results of the analysis of vehicle probe data, for the purpose of identifying the influence areas of intersections. The number of study sites for each type of intersection and available data sources are summarized in Table D-1.

Table D-1. Total number of study sites with attributes

Intersection Control	Data Type	# of Sites	Directions (EB–WB or NB–SB)	Samples	Data Resolution (Hz)
Signal	Trajectory	4	Both	4×2=8	1/3
Stop	Trajectory	7	One	7×1=7	1/3
Roundabout	Trajectory	3	Both	10	1

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Signalized Intersection Site Locations

Data were obtained for a total of four signalized intersection sites, along rural highways, in central Florida (black dots in Figure D-1).

**Figure D-1. Four intersection locations along rural highways in Central Florida**
Source: Map data ©2022 Google

Site 1

Yeehaw Junction (High Truck Percentage)
27.69972777777778, -80.90434444444445

Intersection Attributes

East–West – State Road 60 (Major)
- Speed limit 45 mph in vicinity of intersection
- Two-lane highway and no passing zone, no left/right-turn bays
- Junction for toll highway – located downstream of EB Rte-60
- Seems high traffic of heavy vehicles on East-West corridor
North–South – Hwy 441 (Minor)
- Speed limit: 50 mph in vicinity of intersection
- Two-lane highway, no left/right-turn bays

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-2. Yeehaw Junction Site (map view)**
Source: Map data ©2022 Google

**Figure D-3. Yeehaw Junction Site (State Road 60 – East to West Corridor, High % of heavy vehicles) (satellite view)**
Source: Map data ©2024 Google

Site 2

Bronson Memorial Hwy and Arthur Gallagher Blvd
Multilane Highway – 441 Hwy
28.1918640616823, -81.15464257237842

Intersection Attributes

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

T – signalized intersection
Major road is multilane highway
2 through lanes and one right-turn lane for EB (also bicycle lane)
It is in a school zone
Speed limit: 55 mph

**Figure D-4. Bronson Memorial Hwy and Arthur Gallagher Blvd Site (map view)**
Source: Map data ©2022 Google

Page 45

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-5. Bronson Memorial Hwy and Arthur Gallagher Blvd Site (satellite view)**
Source: Map data ©2024 Google

Site 3

SR-520 and Maxim Parkway Intersection
28.51394398998677, -81.0622791774354

Intersection Attributes

Multilane divided highway
Signalized ‘T’ intersection
Speed limit: 55 mph in vicinity of intersection
2 through lanes, left and U-turn lane on EB approach
2 through lanes, left-turn lane on WB approach

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-6. SR-520 and Maxim Parkway Site (map view)**
Source: Map data ©2022 Google

**Figure D-7. SR-520 and Maxim Parkway Site (satellite view)**
Source: Map data ©2024 Google

Site 4

CR-426 and FL-46, Geneva, FL
28.73337621159619, -81.11514690240303

Intersection Attributes

Major two-lane highway, FL-46, intersection with 1^st Street (minor)
Skewed Intersection
Gas stations and driveways in the vicinity of intersection

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Major street has a dedicated left-turn lane and a shared though-right lane.
Speed limit on major street is 55 mph, but reduced to 45 mph at 1500 ft upstream of the intersection.

**Figure D-8. FL-46 and CR-426/1st Street Site (map view)**
Source: Map data ©2022 Google

**Figure D-9. FL-46 and CR-426/1st Street Site (satellite view)**
Source: Map data ©2024 Google

Stop-Controlled Intersection Site Locations

Data were obtained for a total of seven stop-control intersection sites, along rural highways, in central Florida (orange dots in Figure D-10).

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-10. Seven Stop-controlled intersections in Florida**
Source: Map data ©2022 Google

Site 1

Lake Pickett Road at N Fort Christmas Road, FL
28.59868562737476, -81.07542409814873

Intersection Attributes

Stop-controlled T–intersection.
Dedicated left and right-turn lanes.
Posted speed limit 45 mph.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-11. Lake Pickett Road at N Fort Christmas Road, FL (map view)**
Source: Map data ©2022 Google

**Figure D-12. Lake Pickett Road at N Fort Christmas Road, FL (satellite view)**
Source: Map data ©2024 Google

Page 50

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Site 2

Taylor Creek Road at E Colonial Drive
28.53655356333482, -81.01220531644309

Intersection Attributes

Stop-controlled T–intersection.
Posted speed limit 35 mph.
Major highway is multilane divided highway.

**Figure D-13. Taylor Creek Road at E Colonial Drive, FL (map view)**
Source: Map data ©2022 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-14. Taylor Creek Road at E Colonial Drive, FL (satellite view)**
Source: Map data ©2024 Google

Site 3

S Fort Christmas Road at E Colonial Drive
28.53683001935565, -81.01789051145427

Intersection Attributes

Stop-controlled T–intersection.
Posted speed limit 45 mph.
Major highway is multilane divided highway.

**Figure D-15. S Fort Christmas Road at E Colonial Drive, FL (map view)**
Source: Map data ©2022 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-16. S Fort Christmas Road at E Colonial Drive, FL (satellite view)**
Source: Map data ©2024 Google

Site 4

Taylor Creek Road at FL–520
28.462825456163536, -80.99278804104223

Intersection Attributes

Stop-controlled T–intersection.
Posted speed limit 35 mph.
Major highway is multilane divided highway.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-17. Taylor Creek Road at FL-520 (map view)**
Source: Map data ©2022 Google

**Figure D-18. Taylor Creek Road at FL-520 (satellite view)**
Source: Map data ©2024 Google

Site 5

Deer Park Road at Nova Road
28.282567428223185, -80.92317557563702

Intersection Attributes

Stop-controlled T–intersection.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Posted speed limit 55 mph.
Major highway is two-lane undivided highway.

**Figure D-19. Deer Park Road at Nova Road (map view)**
Source: Map data ©2022 Google

**Figure D-20. Deer Park Road at Nova Road (satellite view)**
Source: Map data ©2024 Google

Site 6

Nova Road at E. Irlo Bronson Memorial Hwy
28.243980091596192, -81.22311904061856

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Intersection Attributes

Stop-controlled T–intersection.
Posted speed limit 55 mph.
Major highway is multilane divided highway.
Dedicated right-turn and left-turn lanes on minor.

**Figure D-21. Nova Road at E. Irlo Bronson Memorial Hwy, FL (map view)**
Source: Map data ©2022 Google

**Figure D-22. Nova Road at E. Irlo Bronson Memorial Hwy, FL (satellite view)**
Source: Map data ©2024 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Site 7

Holopaw Road (US-441 S) at E. Irlo Bronson Memorial Hwy
28.14485532027373, -81.07610174716476

Intersection Attributes

Stop-controlled T–intersection.
Posted speed limit 55 mph.
Major two highways meet (US-441 S with US-192)
Dedicated right-turn and left-turn lanes on minor.

**Figure D-23. Holopaw Road (US-441 S) at E. Irlo Bronson Memorial Hwy, FL (map view)**
Source: Map data ©2022 Google

**Figure D-24. Holopaw Road (US-441 S) at E. Irlo Bronson Memorial Hwy, FL (satellite view)**
Source: Map data ©2024 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Roundabout Intersection Corridor Locations

Test car trajectories data were obtained from NCHRP Project 3-100. Following are the three study sites:

Corridor I: SR–539 in Whatcom County, Washington
Corridor II: Borgen Boulevard in Gig Harbor, Washington
Corridor III: Golden Road in Golden, Colorado

Table D-2. Roundabout sites attributes

Site No.	Road Name	# of Rbts	Arterial # of Lanes	Rbt Lanes	Rbt Diameter (ft) [m]	Posted Speed Limit (mph) [km/h]	Corridor Length (mi) [km]	Area Type
1	SR 539	4	4	2	175 [55]	50 [80]	3.7 [5.95]	Rural / Suburban
2	Borgen Boulevard	4	4	2	175 [55]	35 [55]	1.4 [2.25]	Suburban
3	Golden Road	5	4	2	175 [55]	35 [55]	1.0 [1.61]	Suburban

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Corridor 1

SR-539 in Whatcom County, Washington
48.923033794705546, -122.48568849413243

**Figure D-25. SR-539 in Whatcom County, Washington (map view)**
Source: Map data ©2022 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-26. SR-539 in Whatcom County, Washington (satellite view)**
Source: Map data ©2024 Google

Corridor 2

Borgen Boulevard in Gig Harbor, Washington
47.3598891345255, -122.58960710025757

**Figure D-27. Borgen Boulevard in Gig Harbor, Washington (map view)**
Source: Map data ©2022 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-28. Borgen Boulevard in Gig Harbor, Washington (satellite view)**
Source: Map data ©2024 Google

Corridor 3

Golden Road in Golden, Colorado
39.73532167732723, -105.18428984502994

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-29. Golden Road in Golden, Colorado (map view)**
Source: Map data ©2022 Google

**Figure D-30. Golden Road in Golden, Colorado (satellite view)**
Source: Map data ©2024 Google

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Analysis

Data Attributes

GPS trajectory data: 1 GPS point every 3 seconds – used for signalized and stop-controlled intersections.
Test Car GPS trajectory data: 1 GPS point every one second – used for roundabouts.
Trajectory data advantages: larger dataset and 11 different sites.
Test car data advantages: more than 100 runs on each corridor and three corridors in two different states.
Both datasets are comprised of
- Veh ID,
- Speed in km/h,
- Time stamp with date,
- Latitude/longitude,
- Heading angle.

Pre-Processing of Data

**Figure D-31. Steps to pre-process GPS data**

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Data Filtering

**Figure D-33. Speed profiles along FL-46 (3000 ft upstream & downstream) (speed in km/h on Y-axis)**

Only SE-bound trajectories
Further cleaning was done.

Steps in Data Processing

Computed distance between consecutive points and added cumulative distance column to data.
Added acceleration/deceleration in ft/s² column to data.
Added speed in ft/s column to data.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Influence Area Determination

Developed heuristic algorithm to determine influence area using acceleration / deceleration.

Sample Trajectory, Step 1

Hollow dots are GPS points every 3 seconds.
Black small line indicates STOP Line

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Sample Trajectory, Step 2

Selected 15 points upstream and 15 points downstream of the STOP line.

Sample Trajectory, Step 3

Identified upstream influence area based on speed profile – shown in Figure D-40

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Sample Trajectory, Step 4

Identified Downstream Influence Area based on Speed profile – shown in Figure D-41

Sample Trajectory, Step 5

Red point shows where vehicle was stopped.
Dashed black line represents stop line.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-39. Speed vs distance plot.**

**Figure D-40. Speed vs distance plot for step 3**

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-41. Speed vs distance plot for step 4**

Results

This section provides a summary of the analysis results. The results are presented in separate tables based on intersection control type and the upstream and downstream influence area (IA), as follows.

Table D-3. Upstream IA results for signalized intersection

Site	Dir	N	Mean IA ft (Speed mph)	Std. Dev IA ft (Speed mph)	50^th Percentile IA ft (Speed mph)	85^th Percentile IA ft (Speed mph)
01	NB	56	1239.10 (62.00)	356.68 (8.27)	1223.30 (63.70)	1684.60 (69.58)
	SB	103	1443.40 (64.15)	398.51 (8.64)	1391.90 (62.99)	1869.40 (72.33)
	EB	303	1056.80 (57.19)	396.94 (9.54)	965.29 (56.55)	1534.90 (68.01)
	WB	509	547.55 (42.84)	202.98 (7.17)	502.95 (42.94)	774.90 (50.11)
02	EB	878	877.52 (61.05)	301.88 (7.13)	835.71 (60.64)	1228.10 (68.01)
02	WB	541	799.95 (62.16)	279.48 (7.67)	750.88 (61.56)	1071.10 (70.86)
03	EB	502	867.03 (64.26)	286.60 (6.54)	821.18 (64.42)	1186.10 (70.86)
03	WB	544	891.98 (69.85)	305.88 (7.74)	854.06 (69.43)	1205.40 (77.30)
04	NB	593	927.66 (54.38)	315.83 (6.55)	908.80(55.12)	1270.60 (60.52)
04	SB	644	761.84 (49.57)	208.92 (5.56)	739.40 (49.39)	975.55 (55.83)

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Table D-4. Downstream IA results for signalized intersection

Site	Dir	N	Mean IA ft (Speed mph)	Std. Dev IA ft (Speed mph)	50^th Percentile IA ft (Speed mph)	85^th Percentile IA ft (Speed mph)
01	NB	48	1716.90 (63.36)	546.99 (10.29)	1850.0 (64.42)	2270.70 (73.94)
	SB	100	1798.10 (62.20)	436.52 (6.27)	1830.80 (62.98)	2252.20 (68.01)
	EB	297	650.80 (42.32)	352.98 (7.22)	542.73 (41.51)	1027.0 (50.11)
	WB	470	1535.80 (58.25)	450.90 (8.26)	1573.20 (58.70)	2057.60 (66.57)
02	EB	881	1469.20 (60.41)	519.46(7.06)	1408.10 (60.12)	2128.80 (68.01)
02	WB	557	1224.94 (58.71)	353.25 (6.07)	1187.10 (58.69)	1616.70 (65.14)
03	EB	490	1822.50 (67.01)	459.37 (6.46)	1811.30 (67.28)	2404.01 (73.72)
03	WB	515	1538.20 (64.23)	431.58 (6.12)	1498.90 (64.42)	2056.10 (70.15)
04	NB	592	1060.01 (49.69)	342.02 (5.35)	1044.40 (50.11)	1453.60 (55.12)
04	SB	651	1267.97 (56.26)	366.07 (5.95)	1324.30 (56.55)	1668.50 (62.27)

*IA = Influence Area

Table D-5. Upstream IA results for stop-controlled intersection

Site	Dir	N	Mean IA ft (Speed mph)	*Std. Dev IA ft (Speed mph)**	50^th Percentile IA ft (Speed mph)	85^th Percentile IA ft (Speed mph)
01	EB	131	689.33 (49.62)	255.79 (7.12)	681.50 (48.67)	950.13 (56.54)
02	NB	123	517.28 (44.92)	170.95 (7.54)	482.75 (45.09)	709.75 (52.29)
03	SB	252	735.95 (51.94)	248.08 (7.07)	700.71 (51.89)	1031.20 (59.04)
04	SB	51	599.99 (45.92)	288.35 (7.05)	460.21 (45.09)	999.26 (55.00)
05	NB	20	903.87 (58.94)	309.75 (6.43)	827.90 (59.05)	1289.30 (64.78)
06	SB	22	829.46 (51.24)	309.72 (6.71)	789.79 (50.46)	1205.10 (58.70)
07	NB	526	768.54 (51.62)	210.37 (7.02)	753.15 (52.25)	976.33 (58.69)

*IA = Influence Area

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Table D-6. Downstream IA results for stop-controlled intersections

Site	Dir	Turn	N	Mean IA ft (Speed mph)	Std. Dev IA ft (Speed mph)	50^th Percentile IA ft (Speed mph)	85^th Percentile IA ft (Speed mph)
01	EB	RT	36	1200.00(54.26)	319.82(4.72)	1091.37(54.04)	1695.60(60.20)
01	EB	LT	99	977.53(48.34)	348.69(6.96)	1109.30(46.53)	1330.50(56.54)
02	NB	RT	63	1415.40(61.51)	270.71(7.12)	1409.90(62.27)	1687.50(66.60)
02	NB	LT	33	1332.6(64.07)	282.40(6.98)	1257.10(63.70)	1573.10(72.36)
03	SB	RT	27	1217.20(57.45)	86.87(4.93)	1240.90(57.26)	1302.40(64.02)
03	SB	LT	212	1452.95(61.07)	326.98(6.88)	1469.38(61.56)	1832.77(67.28)
04	SB	RT	12	1589.40(63.70)	282.94(5.78)	1657.60(62.63)	1857.70(69.93)
04	SB	LT	10	1929 (68.43)	481.52 (8.26)	1934.95(68.71)	2556.98(75.87)
05	NB	RT	---	---	---	---	---
05	NB	LT	44	1471.01(59.36)	331.25(6.79)	1427.90(59.05)	1882.30(67.06)
06	SB	RT	11	1232.40(58.88)	229.98(7.60)	1177.30(58.69)	1510.90(67.75)
06	SB	LT	88	1474.40(61.95)	299.77(5.57)	1504.60(62.27)	1805.20(68.00)
07	NB	RT	44	1766.90(65.23)	407.56(6.52)	1728.10(66.57)	2282.30(71.50)
07	NB	LT	474	1785.20(64.69)	390.89(5.39)	1735.90(65.14)	2234.70(70.15)

--- Missing data for right-turn movements

Table D-7. Upstream IA results for roundabout intersections

Site	Dir	N	Mean IA ft (PSL mph)	Std. Dev IA ft (PSL mph)	85th Percentile IA ft (PSL mph)
01	NB	393	627.35 (50)	102.57 (50)	729.50 (50)
02	NB	96	532.40 (35)	182.32 (35)	743.41 (35)
03	WB	139	407.45 (35)	165.03 (35)	588.75 (35)

PSL: posted speed limit.

Table D-8. Downstream IA results for roundabout intersections

Site	Bound	N	Mean IA ft (Speed mph)	Std. Dev IA ft (Speed mph)	85th Percentile IA ft (Speed mph)
01	NB	406	873.86 (50)	192.55 (50)	1068.80 (50)
02	NB	96	446.26 (35)	173.69 (35)	687.03 (35)
03	WB	141	522.42(35)	164.63 (35)	700.29(35)

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Percentile Selection Procedures

Length of Upstream Influence Area

To examine the impact of three different traffic controls (i.e., intersection types), the upstream IA at differences is illustrated in Figure D-42. For instance, 70^th percentile IA lengths for “Stop” control intersection is 800 ft, Signalized Intersection is 1020 ft, and roundabout is 670 ft.

**Figure D-42. Upstream IA lengths of three types of intersection**

Upstream Influence Area: Speed Reduction

To determine the speed drop from running speed of the upstream segment on the approach to intersection, average speed reduction at different locations (different percentile upstream IA lengths) on upstream approach were calculated. Figure D-43 shows the average speed reduction from the operating speed to the distance of specific percentile of upstream IA length. For example, the average speed reduction from the operating speed to the 70^th percentile distance upstream of the stop-control intersection is 3.4 mph, whereas at a 50^th percentile distance the speed reduction is about 4.35 mph. The speed reduction upstream of the roundabout is different from the other two types of intersections because most of the vehicles do not stop at “Yield” line of the roundabout approach.

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

**Figure D-43. Average speed reduction at different percentile distances**

Upstream Influence Area: Average percentage speed reduction

The posted speed limits at different sites were different. Therefore, instead of comparing magnitude of speed reduction for different intersection controls, average percentage speed reduction is a better measure to select an upstream IA length based on percentile length as shown in Figure D-44.

**Figure D-44. Average percentage speed reduction at percentiles distances**

Page 73

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Decision Rule – Upstream Influence Area

Traffic operational analysis is different from safety applications.
- Tangible impact on traffic operations rather than trying to incorporate a vast majority of drivers.
Signal and stop-control require vehicles to stop, a roundabout does not.
Recommended 70^th percentile of IA length for signal and stop-control intersections.
- More than 5% (3 mph) reduction in average speed (≈ 6%).
Recommended 50^th percentile of IA length for roundabouts.
- Corresponds to approximately 4.5% (2.4 mph) average speed reduction.

Downstream Influence Area: Speed difference

Figure D-45 illustrates the speed difference between the downstream approach running speed and the speed at different percentiles IA lengths. For example, the speed at 70^th percentile downstream distance of signalized intersection is about 4.5 mph less than the running speed on downstream segment.

**Figure D-45. Average speed difference from downstream running speed at different percentile distances**

Page 74

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Downstream Influence Area: Average percentage Speed difference

**Figure D-46. Average percentage speed difference from downstream running speed at different percentile distances**

Decision Rule – Downstream Influence Area

Traffic operational analysis is different from safety applications.
- Tangible impact on traffic operations rather than trying to incorporate a vast majority of drivers.
At signal and stop-control, vehicle starts from stop position. At roundabout, vehicle starts from a reduced speed.
Recommended 70^th percentile of IA length for signal control intersections.
- Speed difference is more than 6.5% from the downstream average speed (6.2 mph).
Recommended 50^th percentile of IA length for roundabouts.
- Speed difference is approximately 5.8% (3.1 mph).

Page 75

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Comparison of Upstream and Downstream IAs

Signalized intersection

Roundabout intersection

Page 76

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Stop-control intersection

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Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Influence Area Equations and Look-Up Tables

Upstream IA at Signal Control Intersections

$I . {A.}_{S i g n a l / U p s t r} = - 923.89 + 35.92 \times M e a n S p e e d M P H + 1.23 \times % H e a v y V e h - 374.05 \times I_{m u l t i l a n e}$

[D-1]

Multilane Highways

Mean Speed (mph)	70th Percentile IA (ft)
Mean Speed (mph)	HV 5%	HV 10%	HV 15%	HV 20%	HV 25%	HV 30%
45	325	330	335	345	350	355
50	505	510	515	520	530	535
55	685	690	695	70	710	715
60	865	870	875	880	890	895
65	1045	1050	1055	1060	1070	1075
70	1220	1230	1235	1240	1250	1255
75	1400	1410	1415	1420	1425	1430

Two-lane Highways

Mean Speed (mph)	70th Percentile IA (ft)
Mean Speed (mph)	HV 5%	HV 10%	HV 15%	HV 20%	HV 25%	HV 30%
45	700	705	710	720	725	730
50	880	885	890	895	900	910
55	1060	1065	1070	1075	1080	1090
60	1240	1245	1250	1255	1260	1270
65	1420	1425	1430	1435	1440	1450
70	1595	1600	1610	1615	1620	1630
75	1775	1780	1790	1795	1800	1810

Variable definitions

MeanSpeedMPH = average upstream operating speed (mph)
%HeavyVeh = percentage of heavy vehicles (per HCM definition) in the traffic stream
I_multilane = indicator variable, =1 if upstream roadway has multiple through lanes, = 0 otherwise

Page 78

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Downstream IA at Signal Control Intersections

$I A_{S i g n a l / D o w n s t r} = - 1929.64 + 60.25 \times M e a n S p e e d M P H + 7.23 \times % H e a v y V e h - 154.15 \times I_{m u l t i l a n e}$

[D-2]

Multilane Highways

Mean Speed (mph)	70th Percentile IA (ft)
Mean Speed (mph)	HV 5%	HV 10%	HV 15%	HV 20%	HV 25%	HV 30%
45	660	700	735	770	810	845
50	965	1000	1035	1070	1110	1145
55	1265	1300	1340	1345	1410	1445
60	1565	1600	1640	1675	1710	1750
65	1870	1900	1940	1975	2015	2050
70	2170	2205	2240	2280	2315	2350
75	2470	2505	2540	2580	2615	2650

Two-lane Highways

Mean Speed (mph)	70th Percentile IA (ft)
Mean Speed (mph)	HV 5%	HV 10%	HV 15%	HV 20%	HV 25%	HV 30%
45	815	855	890	925	960	1000
50	1120	1155	1190	1225	1265	1300
55	1420	1455	1490	1530	1565	1600
60	1720	1755	1790	1830	1865	1900
65	2020	2060	2095	2130	2165	2200
70	2325	2360	2395	2430	2470	2505
75	2625	2660	2695	2730	2470	2805

Variable definitions

MeanSpeedMPH = average downstream operating speed (mph)
%HeavyVeh = percentage of heavy vehicles (per HCM definition) in the traffic stream
I_multilane = indicator variable, = 1 if downstream roadway has multiple through lanes, = 0 otherwise

Page 79

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Upstream IA at Stop-Control Intersections

$I A_{S t o p / U p s t r} = - 1147.62 + 38.82 \times M e a n S p e e d M P H$

[D-3]

Mean Speed (mph)	70^th Percentile Upstream IA (ft)
45	570
50	760
55	950
60	1145
65	1335

Downstream IA at Stop-Control Intersections

$I A_{S t o p / D o w n s t r} = - 1067.63 + 44.38 \times M e a n S p e e d M P H$

[D-4]

Mean Speed (mph)	70^th Percentile Downstream IA (ft)
45	930
50	1150
55	1370
60	1595
65	1815

Variable definitions

MeanSpeedMPH = average up/downstream operating speed (mph)

Page 80

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

Upstream IA at Roundabout Intersections

$I A_{R o u d a b o u t / U p s t r} = 402.15 + 10.21 \times M e a n O S m p h - 15.27 \times M e a n C S m p h$

[D-5]

Note: As the data were available for only three sites, models were developed using individual vehicle speeds instead of mean operating speed at each site.

Mean Speed (mph)	50th Percentile IA (ft)
Mean Speed (mph)	CS = 10 mph	CS = 15 mph	CS = 20 mph	CS = 25 mph
35	605	530	455	380
40	660	580	505	430
45	710	635	555	480
50	760	685	605	530
55	810	735	660	580
60	860	785	710	635

CS = mean circulating speed

Downstream IA at Roundabout Intersections

$I A_{R o u d a b o u t / D o w n s t r} = - 313.80 + 32.73 \times M e a n O S m p h - 27.01 \times M e a n C S m p h$

[D-6]

Note: As the data were available for only three sites, models were developed using individual vehicle speeds instead of mean operating speed at each site.

Mean Speed (mph)	50th Percentile IA (ft)
Mean Speed (mph)	CS = 10 mph	CS = 15 mph	CS = 20 mph	CS = 25 mph
35	560	425	290	155
40	725	590	455	320
45	890	755	620	485
50	1050	920	780	650
55	1215	1080	945	810
60	1380	1245	1110	975

CS = mean circulating speed

Variable definitions

IA_Roundabout/_Upstr = Upstream IA of roundabout (ft)
IA_.Roundabout/_Downstr = Downstream IA of roundabout (ft)
MeanOSmph = average up/downstream average operating speed (mph)
MeanCSmph = average roundabout circulating speed (mph)

Page 81

Suggested Citation: "Appendix D: Intersection Influence Area." National Academies of Sciences, Engineering, and Medicine. 2024. Developing a Guide for Rural Highways: Reliability and Quality of Service Evaluation Methods. Washington, DC: The National Academies Press. doi: 10.17226/27897.

The preceding equations were developed based on data from roadways with posted speed limits of 45 mph and higher. Consequently, these equations may yield unreasonable results for roadways with lower posted speed limits. Both the upstream and downstream influence distances are compared against practical minimum influence distances, namely, practical stopping distance for the upstream IA and practical acceleration distance for the downstream IA. In both cases, for simplicity, the reference speed is the posted speed limit.

The calculated upstream IA value should be compared to braking distance, per the following equation, and the maximum value used. Note that this formula is simplified, by assuming level grade.

$B r a k i n g D i s t = \frac{V_{I n i t}^{2}}{2 a}$

[D-7]

Where:

BrakingDist = distance for vehicle to decelerate from speed V_Init to a stop, in feet

V_Init = initial speed, in ft/s; posted speed limit is recommended value

a = deceleration rate, 10.0 ft/s/s, based on Institute of Transportation Engineers (ITE) recommendations for slowing on an approach to a signalized intersection (ITE, 2016)

Likewise, the calculated downstream IA value should be compared to practical acceleration distance, per the following equation, and the maximum value used.

$A c c e D i s t = 0.1655 \times V_{F i n a l}^{2.0917}$