Why Monorail can be up to Three Times Faster in Dense Urban Areas

 

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Monorails will be faster than light rail. Monorails, being grade separated, can reach higher maximum speeds than light rail in non-exclusive right-of-way (i.e., light rail traveling in the street).

Both Monorail and light rail vehicles can typically reach maximum system speeds of 55 MPH or more. However, who would want a 100,000 lb LRT vehicle traveling down Lamar or Guadalupe at 55 MPH inches away from automobiles, pedestrians, and bicyclists?

Light Rail as currently planned for Austin would run in the center of the street. Light rail stations would be located in the center of the street as well. Therefore to access the stations, pedestrians and physically disabled persons must cross lanes of traffic. Light rail vehicles can achieve a typical deceleration (braking) rate of 3.0 MPH/s or an emergency deceleration rate of 4.2 MPH/s.  An emergency stop from 55 MPH would take (time = v / a):

55 / 4.2 = 13.1 s

and the vehicle would travel (distance = 1/2 * a * t**2):

0.5 * (4.2 mi/hr-s *  1/3600 hr/s) * (13.1 s)**2 = 0.10 mi = 528 ft.

This would clearly present a hazard to pedestrians, bicyclists, and motorists. Therefore, LRT travel in non-exclusive right of way is generally limited to 35 MPH or less.

The following study is a gold mine of information on the safety issues and guidelines recommended to integrate light rail transit into city streets:

TCRP Project A-05, Integration of Light Rail Transit into City Streets

Because Monorail typically operates totally grade-separated, Monorail vehicles can accelerate at their maximum system acceleration, typically, about 3.0 MPH/s and completely safely and easily achieve typical maximum operating speeds of 55 MPH even in dense urban areas.

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Monorails will be cheaper than light rail. Since Monorails can safely achieve higher maximum system speeds, fewer vehicles are required to achieve any given headway (headway being defined as the time between arrival of successive trains). Assuming equal cost and capacity between light rail vehicles and Monorail vehicles (an issue we will discuss in a future article), this translates directly into cost savings.

Imagine the dual-beam Monorail guideway as a circle. The Monorail travels 20 miles south along one beam, then turns around and travels North 20 miles to the beginning. If one train services this route and the train travels 20 MPH, then the train will take 2 hours to return to its starting point. The headway is 2 hours.

Two trains each traveling 20 MPH will cut the headway to one hour, but the same one hour headway can be achieved by a single train traveling at 40 MPH. Therefore,  a fewer number of faster trains can substitute for a larger number of slower trains. The passenger carrying capacity is the same.

We now present a simple model showing the positive effects of Monorail being able to achieve a faster maximum speed in dense urban areas.

The following assumptions were used:

System Length: 20 miles of dual-beam guideway, with turn-around

Total Number of Stations: 14

Average Distance Between Stations: 1.54 mi

Dwell Time at Each Station: 30 sec.

Maximum System Acceleration: 1.25 m/s**2 = 2.8 MPH/s

Desired Headway: 10 Minutes

Passengers / Train: 224 (84 Seated, 140 standing, 2.7 ft**2/passenger).

Average Number of Stops Each Passenger Rides: 6

This route is our 'Red' line which bypasses IH-35 along Lamar, Guadalupe, Lavaca, South First, and South Congress. We assume that the Monorail vehicle accelerates at 2.8 MPH/s until it reaches any one of the following maximum speeds. It then decelerates at the same rate in time to reach the next station, where it dwells for 30 seconds. Each passenger is assumed to travel for 6 stops, which is approximately the number of stops from one end of the line to the center, thus simulating a typical commute into the central business district. We then examine the effects of maximum system speed on average speed, average passenger trip time, the total number of trains required and the total number of passengers per hour per direction (pphpd) carried by the system.

 

Keep in mind as you read the chart above that the national average light rail speed (FY2000) was 15.3 MPH in 2000 (source: American Public Transportation Association: Light Rail Summary Data, FY2000.

This would put a light rail vehicle somewhere in the left side of each graph below compared to the Monorail which we will assume has a maximum system speed of 55 MPH.

This leads to the following conclusions:

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The average speed of the Monorail (about 37.5 MPH) is over three times the national average LRT speed of 15.3 MPH. Average speeds of over 40 MPH could probably be achieved with suitable Monorail vehicles.

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Average trip times of under 15 minutes for Monorail could be achieved compared to average trip times of over 25 minutes for light rail- ONE HALF the time!

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Seven trains are required for Monorail vs. 12 trains for LRT, assuming equal capacity.

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Passengers per Hour per Direction  (pphpd) for each system remain approximately constant (over 3000).

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Last updated: 04/13/03.