Question

The road becomes a class-III two-lane highway after reaching a long bend in the road. The speeds don’t typically change off-peak at the transition, and width/clearance/access are consistent after the transition too. There are 50% no passing zones. What is the LOS of the two-lane highway?

Answer 1

As per Highway Capacity manual 2010, Level of serivice for 2 lane highways are determined based on 3 measurement crterias

1. ATS (Mobility Criteria) : It is the ratio of highway segment lenth to that of average travel time taken by the vehicles to traverse it during a designated time interval

2.PTSF (convenience / freedom to maneuver criteria ): it is a surrogate measure represented in percentage of vehicles traveling at headways of less than 3.0s at a representatative loaction of highway segment.

3. PFFS (percent of free flow speed ) :it is the ability of vehicle to travelat or near to the post speed limit.

In case of class 3 highway segments (limited length & passing restrictions are not major concerns) such cases the drivers would like to cruise at or near the speed limit. Therefore , on these highways PFFSS is used to define level of Services.The table attched belows shown LOS criteria for two-lane highways.

LOS	Class 3 highways PFFS (%)
A	>91.7
B	>83.3-93.7
C	>75-83
D	>66.7-75
E	<=66.7