00939809

Component

Traditionally internal-external trips were modeled using regression based trip generation equations and gravity model trip distribution. These models were applied at the cordon, meaning the trip was assumed to originate at the cordon and all information outside the cordon was lost. There are several problems with this including the insensitivity of the model to changes to the network near the cordon that might reroute traffic to a different entering location. Additionally, the models tend to generate too many external trips in the urban center of the model area and not enough in the rural areas near the cordon due to the use of regression trip generation based upon zonal socioeconomic variables. Finally, the use of a gravity model, which distributes trips without regard to direction of travel, causes a somewhat semi-circular distribution when constrained by a cordon line. In fact, as shown by recent surveys conducted in Ohio, traffic crossing the cordon has a directional bias based on the direction of travel at that cordon. The result of this is that routes parallel to and near the cordon will be over-assigned in the traditional model. This paper presents modifications to each component of the traditional cordon line external model that will remedy these problems for those areas that don't wish to expand their data collection burden to areas outside their planning boundaries. In this model, trip distribution is a traditional cordon applied gravity model which is modified by using composite impedance in place of the traditional use of travel time alone. This composite impedance takes into account the bias present due to the direction of travel at the cordon and is equal to the product of travel time and an exponential function of the angular impedance. Angular impedance is defined as the angle between the vector representing the general direction of travel at the cordon and the vector defined by the cordon crossing point and a given internal zone centroid. Application of this model to a small metropolitan planning organization in Ohio showed that the model could be calibrated to simultaneously match the trip length frequency distributions (within prescribed tolerances) of both the composite impedance and the stand alone travel time impedance. This model, when applied, did not result in the over assignment of routes parallel to and near the cordon.

The CD-ROM contains the proceedings of the sixth, seventh and eighth conferences. The eighth conference proceedings were published in October 2001.

English

p. 259-272

2002

Eighth TRB Conference on the Application of Transportation Planning Methods

Figures (10)

Cordon counts; Electrical impedance; Gravity models; Transportation planning; Travel time; Trip distribution; Trip generation

Highways; Planning and Forecasting; I72: Traffic and Transport Planning

TRIS, TRB, ATRI

Mar 21 2003 12:00AM

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