Your State Department of Transportation (DOT) has been given funding for the construction of a new freeway to relieve the congestion on the existing freeway that extends through the downtown section of your community. Construction of the new freeway will begin this year and is expected to take a minimum of three years to complete. In the interim, the DOT has decided to evaluate the most congested section of the existing freeway for immediate improvements that would keep traffic flow at less than capacity on this section while the new freeway is under construction. Your supervisor has given you the task of determining the most economical improvements for the existing freeway, so that operations do not exceed capacity for the next several years. This 3,000-foot section of existing freeway has the following characteristics:

• an interchange density of 1 per mile
• free-flow speeds of 58 mph on the upgrade and 62 mph on the downgrade
• carries 1600 vehicles per hour during the peak hour (in one direction) on a grade of 5%
• four asphalt-paved lanes (two in each direction)
• 11-foot lanes with 1-foot right shoulder lateral clearance to a concrete barrier, a 4-foot median with a concrete barrier
• PHF = 0.85
• 11% trucks, 4% buses and no RVs
• the total right-of-way consists of 64 feet

This assignment is divided into the following parts:

As you complete the following tasks, you will determine the most economical improvements that can be implemented on the existing freeway to delay the onset of capacity flow operations.

Task 1. Calculate the free-flow speed and convert volume (vph) to flow rate (pcphpl) for the existing freeway, in both directions (upgrade and downgrade). You will first need to calculate the upgrade and downgrade heavy-vehicle adjustment factors in order to convert volume to flow rate. For selecting the driver population adjustment factor, you can assume that the traffic is mostly commuters who are familiar with the freeway. Using your calculated free-flow speed, construct an appropriate speed-flow curve of the same shape as the typical curves on the free-flow speed versus flow rate graph. The curve should intercept the y-axis at your calculated free-flow speed. The LOS for the upgrade and downgrade can be determined directly from the graph.

Task 2. Using the anticipated growth rate of 15% per year, determine what the traffic volume and flow rate will be in three years. Then repeat all of the steps in Task 1 except for calculation of the free-flow speed to determine what the LOS will be in three years. How many years will it be until the upgrade section is operating close to capacity?

Task 3. Given that the right-of-way cannot exceed a total of 64 feet, develop possible improvements that will forestall capacity operations on this section of freeway. At a minimum, you should evaluate the effects of changing lane widths, lateral clearances and number of lanes (specifically in the upgrade direction). Setting up a spreadsheet program to calculate free-flow speed and flow rate will make this task relatively straightforward.

Task 4. Estimating costs may prove to be the most challenging part of this exercise. What you need to keep in mind is that the term "estimated" means just that - an estimate. The purpose of this exercise is simply to introduce you to the costs associated with highway improvement projects. Possible resources include cost data manuals (such as the RS Means Cost Manuals), government transportation offices, and the civil engineering department at your university.