2 - Laserfiche WebLink

Home Browse Search

DRAFT November 21, 1995 network, fuel and travel time are saved. There is also a potential safety • benefit in reduced congestion. A. Replication The first series of network assignments was a replication of the existing transportation system usage. The purpose behind the existing system was to arrive at a combination of trip generation rates, trip distribution process and network link attributes that would accurately portray City travel patterns in an assignment. This combination would then be retained for travel demand forecasts. An initial all-or-nothing assignment was made under the assumption that there is currently no location on the street network that drivers intentionally avoid because of a capacity deficiency. The assigned traffic volumes for each roadway segment were compared against actual field counted volume data. Segments whose assigned volumes differed to an unacceptable degree from actual volumes were noted. A series of screen lines was used to check that there was an accurate representation of total volume traveling between one part of the City and another. (A screen line is a line drawn east-west or north-south across the entire City. Traffic volumes on all roadway segments crossing the screenline are totaled and compared to the sum of existing volumes on the same segments.) Adjustments were made to trip generation rates, trip distribution and/or network link attributes, and a new assignment was made. This process was continued until the existing system usage . was satisfactorily replicated. B. Ultimate Forecast The trip generation rates and trip distribution process that were used in the final replication assignment were also used in the ultimate development assignment. Most network link attributes were also retained. However, there were a few notable exceptions. All county roads that had a 55 miles per hour speed in the replication assignment were reduced to 45 miles per hour, because they would now be in fully developed areas. County Road 40 and 221st Avenue, both existing gravel roads, were assumed to be paved and straightened with speeds increased to 45 miles per hour. These improvements seem reasonable to expect as the land adjacent to the two roads is developed. The first ultimate assignment was made on the existing street network with the modifications noted above. The forecast ADT volumes are shown in Figure 3. The results identified system deficiencies, locations where demand exceeded capacity. Two remedies were possible: increase capacity on existing roads or add roads to the system. It was not expected that either could solve all the deficiencies alone, but rather that a combination of the two would be necessary. With this in mind, an attempt was made to identify roadway segments to be added to the • network that would have the greatest impact on the deficient areas, whose addition would have enough effect to at least make it practical to solve the remaining deficiencies with capacity improvements. The options for roadway improvements CTP-230.156 -8- 230-156-80