HomeMy WebLinkAboutSight Distance Certification 121225
129 N. Main St. Benton, AR 72015 * 501-315-2626 * Fax 501-315-0024
Friday, December 12, 2025
City of Littlerock
Department of Public Works
Re: Intersection Sight Distance Certification – 2004 AASHTO “Green Book”
Project: S-2006 Eagle Place
Location: 13700 Alexander Road
Intersection: Unnamed Road-1 (STOP controlled) at Alexander Road (2-lane)
Dear Sirs,
On behalf of [Owner/Developer], we evaluated Intersection Sight Distance (ISD) for the
proposed intersection noted above in accordance with the 2004 AASHTO “A Policy on
Geometric Design of Highways and Streets” (Green Book) procedures for stop-controlled
intersections (Case B: vehicle turning from minor road). The AASHTO method computes
required ISD along the major road using:
where is the major-road design speed (mph) and is the AASHTO gap time (seconds).
1) Design Inputs
• Major road: 2-lane, two-way roadway
• Major road design speed: mph
• Minor road design speed: 25 mph (minor approach design; ISD cases below governed
by )
• Grades: Major road = 2.5%; Minor road approach = 2%
• Traffic control: STOP on minor road (two-way stop assumed)
• Driver eye and object heights: 3.5 ft eye height to 3.5 ft object height (AASHTO ISD).
• Driver position (setback): Sight triangles evaluated from a driver eye point located 18.0
ft back from the edge of the major-road traveled way.
2) AASHTO Case Selection and Gap Times ()
For a STOP-controlled minor road intersecting a 2-lane major road (passenger car), the AASHTO
Case B movements evaluated were:
• Case B1 – Left turn from stop: sec
• Case B2 – Right turn from stop: sec
Minor-road approach grade is 2% (≤ 3%), therefore no additional grade-based time adjustment is
required for the minor approach.
3) Required ISD Calculations
Case B1 (Left turn from stop):
Case B2 (Right turn from stop):
Minimum required ISD along the major road:
• B1 (LT from stop): ≥ 441 ft
• B2 (RT from stop): ≥ 385 ft
4) Certification of Compliance (Provided Sight Distance)
Based on the proposed intersection geometry and the sight-triangle evaluation shown on Plat, the
available intersection sight distance from the minor-road driver position (18-ft setback) meets
or exceeds the AASHTO 2004 minimums listed above for Case B1 and Case B2.
To preserve compliance, the sight triangle area will be maintained free of obstructions that would
block a driver’s line of sight between the 3.5-ft eye height and 3.5-ft object height.
Sincerely,
Kazi Islam, P.E.
Project Engineer
Hope Consulting
501 315-2626 Email: kazi@hopeconsulting.com
License: 20876