I-15/Limonite Ave Interchange
Improvement Project
No-Build Alternative
The purpose of the No-Build Alternative is to determine whether or not the existing interchange is capable of handling the predicted 2040 traffic volumes. This particular interchange is a tight diamond interchange which has four ramps, two on-ramps and two off-ramps. The “Tight” in the name refers to its slim design that requires little right of way and material.
A Synchro analysis was conducted on the existing interchange to determine whether or not it was capable of handling the design year 2040 predicted traffic volumes. As you can see the interchange failed to handle those volumes. This is mainly because the largest traffic volumes were the through movements across the bridge. These movements were being delayed by the high left-turn volumes and the tight-diamond does nothing to divert or remove these turns. This means that this alternative fails the second step of the selection process and will be rejected.
Result: Failed
A Merge/Diverge Analysis is an examination of the impact a ramp is expected to have on freeway flow. This is done by estimating the vehicle densities around either an off-ramp or diverge (Figure 1) or an on-ramp or merge (Figure 2). The existing freeway on- and off-ramps were analyzed for the 2040 design year and it was concluded that with the exception of one ramp at one of the peak hours the ramps are capable of handling the 2040 design year traffic with an acceptable level of service of D or above. At this point in the analysis it has already been determined that the no-build alternative is not viable. This analysis will serve a base to compare the viable alternatives to.
As you can see for both of the traffic analyses the current configuration is not a viable option because of the unacceptable level of service of F. Because of this new interchange types need to be designed that are capable of handling the predicted 2040 traffic volumes.
Figure 1: Diverge Junction
Figure 2: Merge Junction
Viability
Merge/Diverge Analysis
Traffic Analysis
F
F