Jul 21 2011

Opinion: Proposed Roundabout A Traffic Engineering Anomaly?

Statement to City Council by Piedmont Resident Regarding a Roundabout at Moraga & Maxwelton

Concerning PRFO’s Blair Park traffic plan, the proposed mini-roundabout at Maxwelton and Moraga is entirely contrary to the Federal Highway Administration’s Feb. 2010 Technical Summary concerning single lane mini-roundabout intersections.

A search of the Internet reveals that every four-way roundabout in existence is on level ground, has right angle intersections, good visibility in all directions, and sidewalks in all directions. All roundabouts in PRFO Traffic Engineer Michael Moule’s online presentations follow these guidelines, consistent with Federal technical guidelines. Yet for the Maxwelton Moraga intersection, Mr. Moule proposes a roundabout that is entirely contrary to Federal  guidelines and his own previous design work.

No roundabout or mini-roundabout on planet Earth remotely resembles the Maxwelton/Moraga intersection with its seven degree slope, obtuse entry angles, lack of sidewalks and extremely limited sight-lines. The PRFO plan deliberately forces bicyclists to take the lane on a slope and have their bodies used as a means of traffic mitigation. The ELS traffic plan is attempting to cut the speed of Moraga avenue in half, from a 35mph median speed to 17-20mph. If implemented, traffic going uphill will still be about four times faster than the average bicyclist going up that hill. And the loss of Moraga Avenue as an arterial truck route must be addressed.

A 15-minute internet search will confirm my comments tonight. I ask Piedmont staff to make this rudimentary due diligence search and report the findings to Council. The use of this radical traffic experiment proposed by PRFO at Maxwelton and Moraga is grossly inconsistent with standard traffic design guidelines. Piedmont does not normally adopt radical and experimental traffic plans.

Rick Schiller

(This statement expresses the personal opinions of the author. All statements made are the opinion of the writer and not necessarily those of the Piedmont Civic Association.)

2 Responses to “Opinion: Proposed Roundabout A Traffic Engineering Anomaly?”

  1. The FHWA’s guidance on mini-roundabouts (http://safety.fhwa.dot.gov/intersection/roundabouts/fhwasa10007/#s4) includes the following site considerations:

    “Mini-roundabouts are most effective in lower speed environments in which all approaching roadways have posted speed of 30 mph or less and an 85th-percentile speed of less than 35 mph (55 km/h) near the proposed yield and/or entrance line.”

    The environmental analysis of the proposed street changes should evaluate whether this is the case on Moraga and if not, whether the proposed mini-roundabout would still be effective in slowing traffic.

    “Locations with light volumes of minor street traffic may not provide a suitable location for a mini-roundabout. Major street vehicles may become conditioned over time to ignore the intersection control due to a lack of minor street vehicles presence, which requires major street drivers to slow and proceed cautiously through the intersection. One rule of thumb used in the U.K. is to have at least 10 percent of the total intersection volume generated from the minor street. Another measure used in the U.K. is that mini-roundabouts should not be considered at intersections with volumes below 500 daily vehicles on the minor street.”

    The environmental analysis should include the traffic volumes on Maxwelton and Moraga and evaluate whether they are in line with this guidance for mini-roundabouts.

    “Mini-roundabouts are generally recommended for intersections in which the total entering daily traffic volume is no more than approximately 15,000 vehicles.”

    Table 4.2 of Piedmont’s General Plan lists average daily traffic (ADT) counts for Moraga ranging from 11,412 in 1977 to 13,180 in 1994. This means that if the ADT on Maxwelton exceeds about 2,000-3,000 or below 500, the intersection may not meet recommended standards. The environmental report should include traffic counts on Maxwelton and a discussion of whether they meet these standards.

    “Mini-roundabouts should generally be designed to be outward draining to place the central island at the highest point of the intersection for maximum visibility. This technique of sloping outward is recommended primarily because it:

    Promotes safety by raising the height of the central island and improving its visibility;
    Promotes lower circulating speeds;
    Minimizes breaks in the cross slopes of the entrance and exit lanes; and
    Drains surface water to the outside of the roundabout.”

    The proposed mini-roundabout slopes about 7% from east to west. No grading to raise the center island is shown on the plans. Sightlines to the mini-roundabout are also not shown on the plans. The environmental assessment should evaluate whether drivers on Moraga will have adequate visibility of the center island from both directions.

    “Construction costs have ranged from about $50,000 for an installation consisting entirely of pavement markings and signage to $250,000 or more for mini-roundabouts that include raised islands and pedestrian improvements.”

    Costs for the mini-roundabout and other proposed street changes should be included in an independent, expert evaluation of the project’s likely costs by a contractor not affiliated with the project proponents. The City should fully understand the costs of construction and maintenance of the project and require all funding to be in place prior to construction to ensure that the City’s depleted reserves will not be put at risk to cover cost overruns, construction-related litigation, or unforeseen maintenance costs.

  2. PRFO moved the entire project 30 feet to the East so there are 385′ sight lines in both directions from the West Lot exit. PRFO would like cars exiting the west lot to cross over Moraga Avenue heading west back into Piedmont.

    The sight lines at the proposed East parking lot exit, situated across from Maxwelton avenue, are inherently limited and cannot be expanded. This is the fundamental necessity of the Maxwelton mini-roundabout, to sharply reduce traffic speed. PRFO’s need does not negate accepted traffic design criteria.

Leave a Comment