Relationship of Traffic to Highway Design

The major traffic elements that influence highway design are:

• Average Daily Traffic and Annual Average Daily Traffic
• Design Hour Volume
• Directional Distribution
• Percentage of Trucks
• Design Speed

Both ADT and AADT are fundamental measures of traffic flow. To the designer, most significant measure of traffic volume is the design hour volume, a two-way value, which may be determined by multiplying by AADT by a proportional representative of the amount of traffic occurring during the peak hour for an average weekday. This proportional value, known as the K- factor, typically decreases as AADT increases. The value of K ranges between 0.09 and 0.10 for many highways.