While we already have a number for cars per hour that can use a lane, we can’t just apply it to buses. Regardless of whether bike lanes are installed in place of 8-foot parking lanes or up to 11-foot travel lanes, we can assume at least two bike lanes per original lane. A study from Davis, California reports the capacity as 2,600 bicycles per hour per 3.3 feet of lane while most other studies have actually found higher throughputs, so we’ll use this as a lower bound. Vehicle Parking Lane: 792 people / hour Bike Laneīicycle lane throughput varies based on width. So, the 990 spots can be used by roughly 495 cars per hour and given the average occupancy of vehicles at 1.6 persons per vehicle we get: After discussing this with people in the know, I understand the average rate may have gone down a bit, but not significantly, so we can assume it is 2 hours. How many people can benefit from them depends on the average parking duration and average occupancy of vehicles.Ī Seattle Department of Transportation (SDOT) parking study from 2002 shows an average parking duration across all zones at 2.3 hours. Assuming a standard length of 18 feet per parking spot, we have 990 spots. How many parking spots do we have on 4.5 miles of road (per direction)? Given space for crosswalks and intersections, parking can take up about three-quarters of a corridor, or in this case 3.38 miles. We use non-work trips, as work trips likely have a significant highway component where there is no parking regardless. To make sense of this, we start with the average non-work trip length of 4.5 miles based on the PSRC Transportation 2040 Final EIS. Parking only makes sense as a whole corridor, as opposed to as a point. Parking, the topic of never-ending neighborhood feuds and controversies… How many people do actually benefit from a parking lane? This is not as easy to evaluate as measuring the throughput of movement. Vehicle Travel Lane: 1,440 people per hour Vehicle Parking Lane Besides vastly increased safety, this is yet another argument for 25 mph speed limits. Given the average occupancy of vehicles at 1.6 persons (based on the PSRC Transportation 2040 Final Environmental Impact Statement), the throughput is: So at 25 mph, lane capacity is maximized at 900 vehicles per hour. McShane (1998), Traffic Engineering, Prentice Hall) It’s interesting to see that the lower the speed of travel, the more vehicles it can move per hour due to lower following distances: Traffic volume depending on travel speed (Source: Roger P. The most common use of right-of-way, a vehicle travel lane can move between 500 and 900 cars per hour. To understand this problem better, below we will calculate how many people actually benefit from the same 10 feet of right-of-way depending on its use: parking lanes, general purpose travel lanes, bike lanes, bus lanes, and even dedicated space for light rail. The crowding out of these functions by transportation is in part natural, as fueled by growing population, but mostly a function of decades of deliberate car-centric policies. And besides providing a pathway between buildings, it has historically also served as space for markets, social gathering, children’s play areas, and been critical for community building. The many uses of a right of wayįundamentally, right-of-way is just public land. But it is also a sign that we should consider alternative street configurations. This is only the result of a good thing-strong job growth and record-low unemployment. The transportation supply it provides no longer meets the demand as evident by growing congestion. Yet, as the city becomes denser, we are finding this configuration to be inadequate in serving its changing needs. Today, most of this space is dedicated to general purpose lanes and parking and is utilized mostly by single occupancy vehicles. Approximately 35% of the land area of Seattle constitutes public right-of-way.
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