13-12 Traffic

Page 30: The last paragraph refers to adequate sight distance for heavy vehicle access, but the bottom of Page 29 states the design vehicle is a single unit truck. Are these the same vehicles?

RESPONSE 13-12

 

The sight distance evaluation conducted for this project was based upon the methodology published in “A Policy on Geometric Design of Highways and Streets” by the American Association of State Highway and Transportation Officials (“AASHTO”).  According to these guidelines, heavy vehicle adjustments can be applied to the ISD criteria.  There are not heavy vehicle adjustments for the SSD criteria in the AASHTO guidelines.

 

ISD can be adjusted for single unit trucks or for combination vehicles (trucks larger than single unit).  For this project, the sight distance criteria was adjusted for a single unit truck since the majority of the truck traffic assessing the site is expected to consist of single unit trucks.  Had we applied the ISD adjustment for combination trucks, the overall conclusions for ISD would remain the same. There are over 1,000 feet of available sight distance to the east, which will accommodate combination trucks, and 580 feet of sight distance to the west, which meets ISD for a passenger vehicle but does not meet ISD requirements for heavy vehicles. It should be noted that intersection sight distance is met for the passenger cars exiting the site, which is the majority of site traffic.

 

The driveway does meet safe SSD in both directions based on AASHTO guidelines. Stopping sight distance is a function of reaction time and braking distance and indicates that motorists have ample time to react to a vehicle exiting the site driveway. 

 

RESPONDENT:

 

Maureen Chlebek, McMahon Associates

 

DATE:

June 20, 2016