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Transportation Engineering

2010 Fall Semester

Capacity and Level of Service

(Chapter 9)

Level of Service (LOS)

-^

Definition by HCM 2000^ –

Level of service (LOS) is a quality measuredescribing operational conditions within atraffic stream, generally in terms of suchservice measures as speed and travel time,freedom to maneuver, traffic interruptions,and comfort and convenience.

LOS A (Excellent) ~ F (Heavy Congestion)

LOS for Freeway Segments

-^

The objective is^ –

to be able to assess the level of service onfreeway segments and

to design freeway segment to attain aspecific level of service.

By design, it means determining acceptablegrade and width (number of lanes).

Source: http://nexus.umn.edu/Courses/ce3201/CE3201-L2-04.pdf

Freeway Segments

-^

Capacity of Freeway Segments^ –

The maximum sustained 15 min rate of flowin pcphpl (passenger cars per hour per lane)

that can be accommodated by a uniformfreeway segment

under prevailing traffic and roadwayconditions in 1 direction.

LOS for Freeway Segments

-^

Ideal Condition^ –

Lanes are 3.65m wide

Lateral Clearance: There is lateral clearance betweenthe edge of the right (outside) lane and an obstacle2 meters or greater. - Vehicle Equivalents: There are no trucks, buses, RVsor other heavy vehicles in the traffic stream. - Spacing: Interchanges are at least 3 km apart - Grades: Grades do not exceed 2 % - Driver Population: Drivers are familiar with the road(i.e. commuters) - Urban Freeways are 5 lanes in each direction

LOS for Freeway Segments

-^

Flow rate for a basic freeway section^ –

q

= “Analysis Flow Rate” - peak 15 minutep passenger car hourly equivalent flow rate(pcphpl)

l = number of lanes (

N)

f^ HV

,f

p^

= adjustment factors for heavy

vehicles and population

Heavy Vehicle Factor

-^

Passenger Car Equivalents (PCE)^ –

Converting Trucks, Buses and RV's to cars. – Trucks weigh more than cars and have greater difficultymaintaining speed uphill, as a result, they drive slower thancars, and gaps open in front. – Moreover, they are longer and thus take more space. – Trucks and buses have near identical characteristics, so theyare lumped together. RV's are somewhat different (not asheavy as trucks)

Source: http://www.fotosearch.com

Driver Adjustment Factor

-^

f^ P

= Driver adjustment factor

Range of 0.8-1.

Use 1.0 for commuter traffic

If there is significant recreational or weekendtraffic, the value is reduced

Example

-^

Determine the flow rate of a basicfreeway section, given the following info:^ –

15 minute flows = 2000, 1800, 1750, 1700

5 lanes

Trucks and buses = 5%

RVs = 0%

f

p^

Rolling terrain

Example

-^

Determine the number of lanes required tomaintain level of service B on a basic ruralfreeway section, given the following info:^ –

15 minute flows = 2000, 1800, 1750, 1700

Trucks and buses = 15%

RVs = 0%

f

p^

= 0.

Rolling terrain

Lane width: 3.65m

Right Shoulder Lateral Clearance: 1.5m

Interchange spacing: 1 interchange per 2km

Source: http://nexus.umn.edu/Courses/ce3201/CE3201-L2-04.pdf