PASSENGER CAR UNITS FOR HETEROGENEOUS TRAFFIC USING A MODIFIED DENSITY METHOD

The upcoming "Highway Capacity Manual" (HCM) 2000 will use the density method to derive its new, passenger-car equivalences (PCEs) for trucks. The density method assumes homogeneous traffic. Strict lane discipline characterizes homogeneous traffic. By adjusting the density method to handle heterogeneous traffic, one can derive more accurate passenger car units for Indian conditions. Very loose lane discipline describes heterogeneous traffic. Measuring the distribution of each Indian traffic type across the pavement width from different highway types allowed the adjustment. Motorized two-wheelers, cars, bicycles, farm tractors, trucks and other traffic types comprise Indian traffic. Data showed the 85th percentile distribution width of each traffic type can serve as a more accurate measure than the marked lane width when traffic is heterogeneous. The project team collected speed, flow and lateral placement data at 34 rural and suburban highway sites throughout India. These sites comprised six highway types. One can compare two "only passenger car" traffic streams with one being homogeneous and the other heterogeneous. This comparison occurs when the streams have equal average speed and demand. The area density of the heterogeneous traffic stream will be different from the homogeneous traffic stream area density because the pavement widths that each stream uses will be different. This difference results in a "passenger car unit" adjustment factor to convert a passenger car in heterogeneous traffic into its homogeneous traffic counterpart. The study also rendered passenger car units for each Indian traffic type in relation to an Indian passenger car. Preliminary results show the adjustment necessary to convert Indian passenger cars in heterogeneous traffic into U.S. passenger car equivalents for homogeneous traffic. Derivations of passenger-car-unit adjustment factors showed that a car is equivalent to 2 cars in homogeneous traffic on single-lane highways, two-lane highway types without paved shoulders, with 1.5 meter shoulders and with 2.5 meter shoulders. On 1.5 lane highways and four-lane divided highways the passenger-car-unit adjustment factor is 1, i.e., performance of heterogeneous traffic and homogeneous traffic are similar. These equivalents happen when the Indian cars move at the same space mean speed as cars in homogeneous traffic. The modified density method can be used to determine passenger car units for various traffic entity groups on rural and suburban roads in India.

Language

  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 246-257
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00795384
  • Record Type: Publication
  • Report/Paper Numbers: E-C018
  • Files: NTL, TRIS, TRB
  • Created Date: Jul 26 2000 12:00AM