Why a Road Diet won’t work in South O

The city is nearing a  final decision about the “Road Diet”, its proposal to shrink some or all of Coast Highway from 4 lanes to 2 lanes. This is a project that’s been discussed and studied for more than a decade.

Today the city is considering four Alternatives (see here), all of which include a Road Diet with roundabouts. Alternatives 1-3 also include development incentives that could increase residential units 9x and hotel rooms 7x. In July 2017, the city issued a 2,309 page Environmental Impact Report studying Alternatives 1,2,4. In November 2018, it issued a 2,406 page supplemental EIR that studied its new Alternative 3; feedback on the 2018 EIR is due by January 14.

However, neither of the city’s EIRs acknowledge the official “Road Diet” guidance of the Federal Highway Administration (FHWA), as reflected by its November 2014 Road Diet Information Guide. The guide has been available on their website since then, but it is not mentioned in either EIR. According to the Federal guidelines, the existing (and future) traffic levels on Coast Highway are too great for a Road Diet to work here.

What the Guide Says

After reviewing the history of Road Diets over the past 40 years, the FHWA guide talks about the reasons for a diet (Ch. 2), whether a local context is suitable (Ch. 3), how to design a diet (ch. 4) and to measure its success (ch. 5). Only 3 paragraphs of the 72 pages discuss roundabouts; one paragraph recommends against introducing a road diet with roundabouts at the same time due to potential public opposition.

Section 3.3 talks about the operational factors that make a diet suitable or not suitable, based on vehicles per day (VPD) and vehicles per hour per day (VPHPD):

3.3.5 Average Daily Traffic (ADT)

The ADT provides a good first approximation on whether or not to consider a Road Diet conversion. If the ADT is near the upper limits of the study volumes, practitioners should conduct further analysis to determine its operational feasibility. … The FHWA advises that roadways with ADT of 20,000 vpd or less may be good candidates for a Road Diet and should be evaluated for feasibility.

3.3.6 Peak Hour and Peak Direction

The peak hour volume in the peak direction will be the measure of volume driving the analysis and can determine whether the Road Diet can be feasibly implemented. …The Iowa guidelines suggest, from an operational point of view, the following volume-based Road Diet feasibility conclusions (assuming a 50/50 directional split and 10 percent of the ADT during the peak hour):

• Probably feasible at or below 750 vehicles per hour per direction (vphpd) during the peak hour.
• Consider cautiously between 750 – 875 vphpd during the peak hour.
• Feasibility less likely above 875 vphpd during the peak hour and expect reduced arterial LOS during the peak period.

Finally, the guide also says that “Road Diets can cause some diversion of traffic to parallel routes.” In the original EIR, South O and Seaside residents both complained to the city that the Road Diet would cause frustrated drivers to leave Coast for streets paralleling Coast. The 750 vphpd standard means 1,500 vehicles/hour in both directons.

How This Applies to Oceanside

How does this apply to Oceanside? If you look at the November 2018 EIR, Coast Highway peak evening traffic is already above the FHWA’s peak recommended level for Oceanside Blvd. and points south.

Road Diet	none	to Oside Blvd	to Morse	to Morse
Incentives	none	all Coast	all Coast	to Morse
Year	2013	2035	2035	2035
Alternative	Existing	Alt. 1	Alt. 2	Alt. 3
Harbor & Coast	579	704	704	579
Mission & Coast	1,047	1,845	1,845	1,047
Wisconsin & Coast	1,379	1,422	1,422	1,379
Oceanside & Coast	1,638	1,570	1,570	1,638
Morse & Coast	1,510	1,847	1,847	1,510
Cassidy & Coast	1,572	1,646	1,646	1,572
Vista Way & Coast	1,664	1,947	1,947	1,664