Performance Measures on

Two-Way, Two-Lane Highways

HCM Performance Measures

Class I Class II Class III

Source: Manual, H. C. (2010). Highway capacity manual. Washington, DC.

Shortcomings of HCM methodology

Surrogate measure of HCM based on 3-sec headway used for measuring PTF in

the field

Discrepancies between HCM analytical models and the headway-based

method

To address this issue researchers suggested alternative performance measures

Any measures contributing to formation of platoons can be potentially used as

a TWTLHW performance measure.

Example of an Alternative Performance

Measure

Al-Kaisy, Freedman (2010)

𝑃𝐼 = 𝑃𝑝 𝑃𝑖 𝑃𝐼 = 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑖𝑚𝑝𝑒𝑑𝑒𝑑

𝑃𝑝 = 𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑎 𝑣𝑒ℎ𝑖𝑐𝑙𝑒 𝑏𝑒𝑖𝑛𝑔 𝑝𝑎𝑟𝑡 𝑜𝑓 𝑎 𝑝𝑙𝑎𝑡𝑜𝑜𝑛 𝑢𝑠𝑖𝑛𝑔 𝑡𝑖𝑚𝑒

ℎ𝑒𝑎𝑑𝑤𝑎𝑦 𝑑𝑒𝑓𝑖𝑛𝑖𝑡𝑖𝑜𝑛 𝑜𝑓 𝑝𝑙𝑎𝑡𝑜𝑜𝑛

𝑃𝑖 = 𝑡ℎ𝑒 𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑎 𝑣𝑒ℎ𝑖𝑐𝑙𝑒 𝑏𝑒𝑖𝑛𝑔 𝑖𝑚𝑝𝑒𝑑𝑒𝑑 𝑎𝑛𝑑 𝑡ℎ𝑢𝑠 𝑡𝑟𝑎𝑣𝑒𝑙𝑖𝑛𝑔

𝑎𝑡 𝑎 𝑠𝑝𝑒𝑒𝑑 𝑙𝑒𝑠𝑠 𝑡ℎ𝑎𝑛 𝑖𝑡𝑠 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑠𝑝𝑒𝑒𝑑

Example of an Empirical Model

Predicting LOS measure

Source: Polus, A., & Cohen, M. (2009). Theoretical and empirical relationships for the quality

of flow and for a new level of service on two-lane highways. Journal of Transportation

Performance Measures Identified in the

Literature

Performance Measure Study

Percent Following Al-Kaisy and Durbin (2008)

Percent Impeded Al-Kaisy and Freedman (2010)

ATS and PTSF Romana and Perez (2006)

PTSF (based on queuing theory) Cohen and Polus (2011)

Average Travel Speed

Al-Kaisy and Karjala (2008)

Average Travel Speed of passenger

cars

Average travel speed as a

percentage of free-flow speed

Percent follower

Follower density

Polus and Cohen (2009)

Flow

Freedom of flow

Average platoon length

Traffic intensity

PTSF

ATS Brillon and Weiser (2006)

Recommendations for Future Research

No consensus on what threshold should be used for separating platoons. For

Example:

HCM 1985, Al-Kaisy and Durbin (2008) : 6 sec

HCM 2000, Cohen and Polus (2011) : 3 sec

Research topic: what headway threshold can best differentiate the platoons?

Different countries use different LOS measures:

Germany: ATS (Brillon and Weiser (2006))

South Africa: Follower density (Van As (2003))

HCM may not be applicable to certain road environments, therefore studies on TWTLHW

should be conducted to find the most suitable LOS measure

Thanks For Your Attention