picture

Traffic Analysis / Modeling

Overview

To accurately assess and improve the traffic conditions at Railroad Canyon Road and the I-15, different types of analysis must be done. Through the use of Synchro Studio 8 we were able to analyze and optimize the configuration and signaling of the various intersections. Our analysis below displays the advantages of the Diverging Diamond Intersection (DDI), the Continuous Flow Intersection (CFI) and the Single Point Urban Interchange (SPUI).

Scope

The scope of work is to evaluate and improve the intersection level of service. To achieve this goal Synchro Studio was used to model the intersections. Synchro allows the adjustment of traffic volumes, lane configurations and signal timing to obtain overall operations and monitor conditions. With the improved intersection designs and signal timing, major traffic concerns were alleviated which provided an easier commute for the residents of Lake Elsinore. Freeway analysis consisted of calculations for basic freeway segments, merging/diverging influence areas, and weaving segments. Local analysis consist of the new traffic policy directive, intersection control evaluation (ICE).

Diverging Diamond Interchange

A Diverging Diamond Interchange (DDI) is a unique type of intersection configuration where a non-freeway street crosses over to the opposite side when encountering the freeway section. Doing so allows for less of a conflict between left, right and through moments. Ramps both exiting and entering the freeway are split at the interchange, creating dedicated turning lanes onto the street and separating traffic so as to not spill onto the freeway. The signals at the intersection will then only be for singular movement and stop vehicles with oncoming conflicts. Through movements on the street allow for less vehicle storage from nearby intersections but can be mitigated with coordination.

ddi_map ddi_chart

Below is the video modeling for this alternative.

Continuous Flow Interchange

When a traffic model has a high amount of left turn movements a Continuous Flow Intersection (CFI) can be used to mitigate congestion. The unique aspect of a CFI is that it shifts the left turn traffic to the opposite side of the road while keeping the through traffic on its appropriate side. This is very helpful because it allows through traffic and left traffic to move at the same time. One of the main reasons that signals have long cycles is that through traffic and left turns usually need to have their own separate phases to move. The CFI eliminates that extra phase at the ramps while also providing much more left turn storage.

cfi_map cfi_chart

Below is the video modeling for this alternative.

Single Point Urban Interchange

Sometimes cities outgrow their original intersection layouts and cause backups to occur because of short intersection spacing. When intersections are too close to each other, only a small portion of cars are allowed through the intersection since there is not enough space at the next light. When more cars approach an intersection than exit it, traffic will build up at that intersection. The Single Point Urban Interchange (SPUI) is an excellent solution to the problem of short intersection spacing. Through unique layouts and innovative ramp design, the SPUI combines 2 intersections into 1 efficient intersection. The advantage of using the SPUI is increased intersection spacing that allows for more vehicle storage. This increase of storage allows for much higher volume to move through the intersection in the same amount of time as 2 separate intersections.

spui_map spui_chart

Below is the video modeling for this alternative.

Projected / Future Volumes

The turning movement and ramp volumes used were provided to us through our representatives at Caltrans. We received volumes for 2013 and 2040 for the ramps and local turning movements. However, these movements were for the "No Build" case, which shows us what the intersections could be if no improvements occur from now until 2040. Since the Franklin Design Team plans on creating a new interchange with the I-15 we needed to adjust the traffic volume to reflect that. With the help of the Franklin team we worked on analyzing the surrounding area to find which turning movements can be reduced by the new interchange and how much those movements will be reduced. Using those new volumes we were able to accurately assess the situations with our different alternatives and find out which alternative was preferred.

Basic Freeway Segments

Basic freeway segments are located outside of the influence zones of ramps or weaving areas of the freeway. Traffic flow within these basic segments can greatly vary depending on several factors including: volumes, speed, grade, interchange spacing, freeway geometry, etc. The performance of traffic flow, level of service (LOS), is dependent on these factors and is represented by density, vehicles per mile. The LOS for the I-15 was calculated for the basic freeway segments beginning from the adjacent interchanges to Railroad Canyon Road, and is shown below. The LOS was determined for 3 independent cases, (1) the existing (2009 year) volumes/geometry, (2) the project (2040 year) volumes and existing geometry, and (3) the project (2040 year) volumes and ultimate build out of the freeway. The table below shows that the additional HOV lane will help relieves traffic congestion; however, it is recommended that Caltrans perform additional planning to improve the projected (2040) LOS along the I-15.

LOS_chart

Merging / Diverging Influence Areas

Merging/diverging influence areas were calculated using the methodology described in the Highway Capacity Manual 2000 (HCM 2000). These influence areas are located on the mainline at the on-ramps and off-ramps of a local street interchange. The merge influence area at an on-ramp includes the acceleration lane(s) and the 2 lanes immediately adjacent to the acceleration lane for a distance of 1,500 feet downstream from the merge point (where the acceleration lane(s) and mainline lanes starts to become parallel). The diverge influence area at an off-ramp includes the deceleration lane(s) and the 2 lanes immediately adjacent to the deceleration lane for a distance of 1,500 feet upstream from the diverge point (where the deceleration lane(s) and mainline lanes cease to be parallel).

The purpose of merge and diverge analysis is to provide a level of service (LOS) of the merge/diverge influence area. The LOS is calculated based on the density of the influence area. The density is calculated using a methodology provided by the HCM 2000 that includes influential factors such as volumes of ramps and freeway segments, acceleration and deceleration lengths, upstream and downstream ramp distances, etc. This analysis was performed for the case of 2040 Franklin Street interchange alternative with 2040 Railroad Canyon Road No-Build. Due high volume of vehicles on the mainline (major factor in merge / diverge calcs), the merge / diverge calcs resulted in either a D or F for all project alternatives. This team recommends that Caltrans revisit their strategy for widening the I-15, which will increase the merge / diverge LOS for all alternatives.

spui_map