What do recent traffic studies tell us about West Hollywood?
This report explores three recent traffic studies conducted in West Hollywood as part of the City’s development review process. The proposed developments are:
- Robertson Lane Hotel on Robertson and La Peer near Santa Monica Boulevard
- 8555 Santa Monica mixed-use project at Santa Monica & West Knoll
- Arts Club at Sunset & Hilldale
We’ll start with the narrow question of the projects’ traffic impacts, then look at broader numbers. All three projects are on the city’s westside, so we’ll focus on westside traffic.
Significant project impacts
The primary goal of the studies was to determine whether the projects will have a significant impact on traffic at nearby intersections. Each intersection was judged on its own.
The City defines what “significant” means. West Hollywood has chosen thresholds based on traffic delays caused by a project. It’s the extra delay for the average driver in one of the peak hours. It has to be at least 8 to 12 seconds for congested intersections of two commercial corridors and 5 to 8 seconds for other congested intersections. Some cities, such as Santa Monica and Berkeley, have chosen more stringent thresholds.
Using the City’s thresholds and a computer model of traffic, the studies found significant impacts at only two intersections. The first is Santa Monica & Robertson, because of the Robertson Lane Hotel. The project is expected to add 12 seconds of delay for the average car going through the intersection in the mid-day peak and 25 seconds in the PM peak. With that extra delay, the intersection would be graded F for its level of service (LOS) in the PM peak.
The consultant believes they have identified a mitigation measure that can reduce the hotel’s impact to a less-than-significant level. In fact, they claim it will shrink the delay at that intersection almost back to its 2015 level.
The second intersection is Holloway & Hancock, due to the 8555 Santa Monica project. The project would add 10 seconds of delay for drivers on Hancock in the evening peak. However, a closer look at the numbers suggests it’s more about the intersection and the calculations than the project. The computer model says that, in the future, turning from Hancock onto Holloway will be much more difficult in the evening peak. Under those conditions, even one or two extra vehicles from the project making that turn would be significant according to the City’s criteria.
The consultant believes the impact is unavoidable. The City Council will have to decide whether there are “overriding considerations” that merit project approval despite the impact.
Now we’ll look at the broader traffic numbers. The studies estimated the current delay for the average driver at selected intersections during the AM, mid-day, and PM peak hours. The estimates came from computer models, not people with stopwatches.
Sunset & La Cienega is in the lead. According to one of the studies, that intersection imposes close to three minutes (166 seconds) of delay for the average driver in the PM peak. The delays are smaller but still sizable earlier in the day: one minute in the morning and one-and-a-half minutes during the mid-day peak.
Santa Monica & Doheny and Santa Monica & Westbourne come next on the list. Santa Monica & Doheny has over two minutes of delay in the AM peak. Santa Monica & Westbourne has an average delay of one-and-a-half minutes in the PM peak.
Existing level of service
The delays can be represented as A-to-F grades for each intersection’s level of service (LOS). The map below shows the LOS for selected intersections during their lowest-graded peak hour (AM, mid-day, or PM). All of these intersections have traffic signals. Three of them (in red) get an F based on the delay numbers. Two more (in pink) get an F because of in-person observations by the consultants.
LOS A, B, and C are considered, respectively, excellent, very good and good. The lower LOS grades are defined as:
- D = “FAIR. Delays may be substantial during portions of the rush hours, but enough lower volume periods occur to permit clearing of developing lines, preventing excessive backups.”
- E = “POOR. Represents the most vehicles intersection approaches can accommodate; may be long lines of waiting vehicles through several signal cycles.”
- F = “FAILURE. Backups from nearby locations or on cross streets may restrict or prevent movement of vehicles out of the intersection approaches. Tremendous delays with continuously increasing queue lengths.”
Future increases in delays
The studies made traffic forecasts for a few years in the future (2019 or 2020). The forecasts are based on existing traffic, plus “ambient” growth of 1% a year, plus trips from the project being studied, plus trips from other approved or proposed projects in the area. There are 55 to 191 of those “related” projects, depending on the study.
The biggest potential increase in delay is at Sunset & La Cienega. The forecasts suggest that average PM-peak delays could increase by two minutes, from about three minutes to roughly five minutes per driver. The forecasts also suggest an extra minute of delay at each of the intersections where La Cienega meets Holloway, Santa Monica, and Melrose. That would double the delays at those intersections.
The forecasts are probably too high for 2019/2020, because some portion of the related projects won’t be approved or built in the next three years. Nevertheless, the forecasts give a sense of the longer-term congestion and delays that may come from continued traffic growth. We won’t try to guess how future technology — such as self-driving cars — could affect the numbers.
Future level of service
With the future growth in traffic, six intersections would be newly graded F: Santa Monica & Robertson, Santa Monica & San Vicente, Santa Monica & La Cienega, Holloway & La Cienega, Melrose & La Cienega, and Beverly & Doheny. It’s unlikely to happen by 2019/2020, but it may be coming.
Delays have economic and environmental costs. We can get a sense of the total delays at a given intersection by multiplying the delay per driver by the number of drivers. For example, the current total delay at the Sunset & La Cienega intersection in the PM peak hour is:
That’s about 150 hours of delay in that one hour at that single intersection. We don’t know what the total is over a 24-hour period. We do know it’s close to 50 hours in the AM peak hour and 80 hours in the mid-day peak hour.
We can do the same calculation for the future. Please keep in mind that delays can rise faster than traffic volumes, because congested intersections have trouble handling additional vehicles. The forecasts suggest total delays at Sunset & La Cienega could increase to 160 hours in the AM peak hour, 300 in the mid-day peak hour, and 370 in the PM peak hour. The rise in mid-day delays stands out.
For an analysis of how delays may increase citywide, see our report based on an earlier, citywide traffic study.