Note that it is not appropriate or possible to directly compare the Level of Service grade of one type of intersection (e.g., signalized) with another type (e.g., unsignalized).
Key Corridors
Figure 4-7
SOURCE:
Robert L. Harrison, City of Larkspur Traffic Mitigation Fee Program, Final Project, November 1988 |
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Note: Service Level is not shown for intersections operating at LOS C or better. Highway 101. Route 101 is usually quite congested in the vicinity of the Sir Francis Drake Boulevard interchange (also called the Greenbrae interchange), especially north of the interchange going up Cal Park Hill. Traffic from the northbound Sir Francis Drake Boulevard on-ramp merging onto the freeway exacerbates the capacity-reducing impact of the upgrade. In the southbound direction, there are conflicts between traffic entering the freeway and cars exiting at Lucky Drive. At the Lucky Drive interchange, the southbound on- and off-ramps meet Fifer Avenue and Nellen Avenue at the ramp terminus, resulting in difficulty for through-traffic on Nellen. Recent Caltrans studies indicate that there is little excess capacity on the freeway on the Greenbrae interchange ramps as they are currently configured. The 1987 volume south of the interchange was estimated by Caltrans to be 160,000 vehicles per day; north of the interchange Caltrans estimates 135,000 vehicles per day. Sir Francis Drake Boulevard. This is a key east-west through-road in Marin County, stretching from Point Reyes on the west to the San Quentin Peninsula on the east. In the Larkspur Sphere of Influence, it begins on the west at the boundary with Kentfield as a four-lane, undivided roadway with some twists and turns, but becomes divided on the approach to College Avenue. In the commercial area east of College Avenue near the College of Marin, limited on-street parking is allowed. Further east, Sir Francis Drake passes the Bon Air Shopping Center, where significant turning traffic tends to cause delays in through-traffic flow. As the road approaches the Greenbrae interchange, only the left lane continues through to East Sir Francis Drake Boulevard - the right lane becomes the southbound Route 101 on-ramp. For westbound traffic near the interchange, only one lane serves through-traffic, while two left-turn lanes lead to the southbound on-ramp. The interchange itself is an intricate assembly of ramps that separates conflicting traffic flows, with some non-standard characteristics. For example, traffic desiring to proceed northbound on Route 101 from the Redwood Highway on ramp just south of the Greenbrae interchange must first cross Sir Francis Drake Boulevard at grade. This additional traffic tends to degrade the Level of Service at this intersection to the D level currently experienced. Just east of the interchange, East Sir Francis Drake Boulevard has two through lanes in each direction and a median as it passes the Golden Gate Transit Ferry Terminal and the Larkspur Landing mixed use development. East of Larkspur Landing, Drake becomes a two-lane undivided roadway with refuge for left-turning traffic. It continues past the State prison and intersects with Andersen Boulevard in San Rafael, then leads directly onto the I-580 eastbound on-ramp and the Richmond-San Rafael Bridge. On Sir Francis Drake Boulevard, morning traffic flow is heavy, but not gridlocked. The area in front of the Bon Air Shopping Center (near Eliseo Drive), tends to experience some back-ups. In the evening, the situation is much worse, with long back-ups from Wolfe Grade eastward to the freeway. On the east side of the Greenbrae interchange, traffic also backs up through the old railroad trestle from a combination of traffic from the Golden Gate Transit Ferry Terminal, Larkspur Landing, and traffic heading from the Richmond-San Rafael Bridge towards Route 101 southbound. Average daily traffic volumes in 1988 on this road ranged from about 20,000 at the eastern city limit to about 52,000 just east of Eliseo Drive. In particular, the intersections of Sir Francis Drake Boulevard with La Cuesta Drive and Eliseo Drive are either approaching or at capacity (LOS F - see Figure 4-8). Other locations of concern are unsignalized intersections where turning traffic from the minor street has difficulty finding a gap - Larkspur Landing Circle (east), Andersen Drive, and El Portal. Magnolia Avenue. Magnolia Avenue begins north of the City of Corte Madera, at the intersection of Branch Avenue. South of this intersection, this non-freeway north-south corridor parallels Route 101, taking the name Corte Madera Avenue, Camino Alto, and Miller Avenue. For travelers to and from Larkspur, the combination of Magnolia Avenue and Redwood Avenue/ Tamalpais Drive (in Corte Madera) provides convenient access to Route 101. Northbound Magnolia Avenue first passes through the older Downtown area where it is a two-lane, slow moving facility with many driveways and intersections (most of which are stop-sign controlled) and on-street parking. Intersections in this area are tightly spaced (sometimes less than 200 feet apart), and left-turn pockets are not provided. There are also numerous pedestrian crossings, especially in the Old Downtown. These conditions combine to create congestion, where it is often difficult for pedestrians to cross, and where turning vehicles cause long queues because they do not have the protection of a turn lane. The Average Daily Traffic (ADT) on Magnolia Avenue in the vicinity of King Street was about 12,000 in 1988, a heavy volume for a constricted two-lane roadway. North and west of Doherty Drive, Magnolia Avenue becomes more free-flowing, with fewer intersections and driveways. Further along, Magnolia Avenue runs through another commercial area, also with on-street parking, although the roadway is somewhat wider than in the Downtown area, and congestion is less. At the city limit, Magnolia Avenue becomes College Avenue, where it passes the College of Marin to end at Sir Francis Drake Boulevard. The ADT at this northern terminus was about 14,500 in 1988. Only the Corte Madera Avenue/Redwood Avenue intersection (not in the city or its Sphere of Influence) is rated in the unacceptable range (LOS F, see Figure 4-8, page 63). However, traffic conditions through Downtown Larkspur are cause for concern because of restricted room to maneuver, sight-distance problems, and the pedestrian/auto interface. In response to these problems and recent accidents, the City changed the traffic control at the Magnolia Avenue/King Street intersection (adjacent to City Hall) to all-way stop control. (Previously Magnolia Avenue traffic did not have to stop.) This configuration tends to cause congestion at this location, with queues sometimes extending to adjacent intersections. However, it is easier for pedestrians to cross Magnolia Avenue. Many times each year, Magnolia Avenue is gridlocked when traffic diverts from Highway 101 because of an accident. Doherty Drive. This corridor provides both local access for community facilities (e.g., Piper Park, Redwood High School, Henry C. Hall School, the Twin Cities Police Department) and several residential neighborhoods, and also serves as a through facility between Larkspur and Highway 101. The eastern portion of this through corridor passes through the neighboring city of Corte Madera, via Lucky Drive, Fifer Avenue, and Nellen Avenue. The ADT in the Larkspur portion of this corridor at Larkspur Plaza was about 8,800 in 1988. At its western terminus, Doherty Drive is a wide, two-lane facility, with pedestrian crossings near the Hall School (at Larkspur Plaza Drive, and at Larkspur Boardwalk). Further east is another pedestrian crossing at Riviera Circle, serving the high school. This intersection also has four-way stop signs to provide the necessary control for pedestrians to cross safely. Just east of Riviera Circle is the Corte Madera city limit beyond which travelers to the freeway must turn left onto Lucky Drive. An additional turn onto Fifer Avenue is required for freeway traffic. There, southbound traffic can enter the freeway ramp directly, while northbound traffic must use Nellen Avenue to circle under the freeway to Redwood Highway, where the Industrial Way ramp is used. Traffic generally flows reasonably well along this corridor, despite the twists and turns and stop sign controls. The heaviest flow occurs between 7:30 and 8:00 AM and between 3:00 and 3:30 PM, related to the start and end of the school day. Two intersections operate at LOS F, Fifer Avenue at Nellen Avenue (in Corte Madera), and Industrial Way at Redwood Highway (at the northbound freeway ramps). Both of these intersections are unsignalized. Wolfe Grade. Wolfe Grade is a two-lane, undivided, winding, hilly road that connects Sir Francis Drake Boulevard to downtown San Rafael at D Street. It had a 1988 ADT of 13,700, and is often used, in conjunction with Sir Francis Drake Boulevard, to bypass Highway 101 when the freeway is congested. Bon Air Road. Bon Air Road is a two-lane divided roadway where it passes Marin General Hospital. Just north of the hospital, it becomes a four-lane divided road. It serves mainly to connect Sir Francis Drake Boulevard with Magnolia Avenue, and provides access to Marin General Hospital and the residential neighborhood on Bon Air Hill. Madrone Avenue. This road is narrow and winding, and serves many homes west of Magnolia Avenue. Portions of the road are paved around old redwood trees. Redwood Highway. This road parallels Highway 101 on the east side, serving as part of the Doherty/Lucky/Fifer/Nellen/Redwood freeway access. It also serves the industrial land use, trailer park, and Greenbrae Boardwalk, east of Highway 101.
Traffic Accident Patterns While this is not a definitive accident study, it does indicate the relative level of accidents at key locations in the city. The highest number of accidents over the five-year period occurred at the intersection of Sir Francis Drake Boulevard with the Route 101 northbound ramps (78 accidents, compared to an average of 22 per intersection). At this intersection, the high traffic volumes, combined with confusing geometrics and narrow channels under the railroad trestle, create hazardous conditions. |
| Intersection | Total |
| Magnolia at: | |
| Piedmont | 11 |
| Baltimore | 7 |
| Madrone | 17 |
| King | 27 |
| Cane | 21 |
| Ward | 32 |
| Doherty | 31 |
| Bon Air | 28 |
| Dartmouth | 21 |
| Frances | 9 |
| Estelle | 8 |
| Murray | 12 |
| Sir Francis Drake at: | |
| El Portal | 10 |
| Eliseo | 19 |
| NB 101 Ramps | 78 |
| Larkspur Landing Circle (W) | 11 |
| Larkspur Landing Circle (E) | 57 |
| Doherty at: | |
| Larkspur Plaza | 19 |
| Redwood High School | 7 |
| Riviera Circle | 8 |
| Bon Air at: | |
| South Eliseo | 15 |
| Intersection Average | 22.4 |
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______________________________ The second highest accident location was Larkspur Landing Circle (east) at Sir Francis Drake Boulevard. A traffic signal has since been approved for this location, with installation scheduled for January 1991. Other locations where the accident frequency was above the city average are clustered on Magnolia Avenue, in the Downtown area, and near Bon Air Drive.
Projected Future Conditions The results of the Harrison study were summarized in the background document, Larkspur General Plan Circulation Report, which is part of the General Plan Technical Appendix. This information, together with discussions at several citizens' committee meetings, was used to develop the Goals, Policies, and Programs of the Circulation and Land Use chapters. State law requires that the Circulation and Land Use elements be internally consistent. This was in part accomplished in Larkspur by coordination between the Land Use and Circulation sub-committees during the plan development process. The implications of the land use plan were then evaluated using a local area traffic model for the City of Larkspur and its environs.
Model Method and Assumptions
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Figure 4-10
Trip Distribution Assumptions
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