*Takes a deep breath* - A few things...
Firstly, these aren't all "sh*tty, 100 year old trolleys". The ones purchased from Portland are vintage replicas built in the 90's. Those are what's currently being tested on the street, I believe. The third car expected to be used is a Melbourne W2, one of three purchased. These are much older, built in the 1930's. They were known for having braking issues, but Melbourne upgraded the cars' brakes around 2001-2003. I don't know if the Loop Trolley's car is one that was refreshed, though. If not, that could be what he was talking about but it's reported that the three they bought were in use until 2005 so it's feasible they have the improved braking system.
Secondly, I think there must be some acknowledgement that any trolley won't stop as fast as a car, period. It's simply physics; they're heavier, and steel wheels on steel tracks just don't have the same grip as rubber wheels on asphalt or concrete. Cincinnati's Go Metro line (using modern streetars) acknowledges this, for example:
To nerd out a bit, most streetcars have two or three braking elements. Wheel brakes press a steel brake against the wheels themselves to slow down. This is the primary brake for most streetcars. It's not very efficient though; while cars have eight wheels, and brakes can be applied against all of them at once, their contact patch (where the wheel meets the rail) is tiny compared to a car's wheels.
Because of this most streetcars also employ track brakes. This is either a steel or wooden bar that can be installed between the wheels on the bogies or on the chassis itself that can be pressed into the track to provide additional friction. Those aren't applied by default; only when additional braking is needed. They can be used in an emergency braking situation or when traversing steep inclines (not a problem here, obv.). Based strictly on photos, it appears the trolleys from Portland do have track brakes, but I'm not sure that the W2 cars do.
Some cars also have a last-resort emergency brake called a wedge brake. If that's engaged the car drops a steel wedge between the wheels and the track. The pressure and friction of the car during a wedge-brake can actually weld the wedge to the track, so it's only used if absolutely needed. I don't know whether any of these cars have wedge brakes, though since the Portland cars are newer I'd think it's possible.
We don't know if that '70' at 15 mph' figure, assuming it's accurate, is against wheel braking only or if that factors in an available track braking.
Thirdly, does anyone know if the 70' stopping distance at 15 MPH includes reaction times? The National Association of City Transportation Officials have published a chart of braking and stopping distances for vehicles on their site. According to that, a vehicle travelling at 15 mph needs only 11' to stop, but factoring in response time increases that to 44'. 70' is worse, obviously, but if response time is factored in that's actually not horrible for a streetcar given the inherent braking deficiencies mentioned above.
*phew*. Hope at least some of you made it through all that.
-RBB
Firstly, these aren't all "sh*tty, 100 year old trolleys". The ones purchased from Portland are vintage replicas built in the 90's. Those are what's currently being tested on the street, I believe. The third car expected to be used is a Melbourne W2, one of three purchased. These are much older, built in the 1930's. They were known for having braking issues, but Melbourne upgraded the cars' brakes around 2001-2003. I don't know if the Loop Trolley's car is one that was refreshed, though. If not, that could be what he was talking about but it's reported that the three they bought were in use until 2005 so it's feasible they have the improved braking system.
Secondly, I think there must be some acknowledgement that any trolley won't stop as fast as a car, period. It's simply physics; they're heavier, and steel wheels on steel tracks just don't have the same grip as rubber wheels on asphalt or concrete. Cincinnati's Go Metro line (using modern streetars) acknowledges this, for example:
^ bolds mine.Pedestrians should exercise extra caution around the streetcar. Even at posted un-signalized crosswalks, the streetcar has a greater stopping distance than other traffic.
To nerd out a bit, most streetcars have two or three braking elements. Wheel brakes press a steel brake against the wheels themselves to slow down. This is the primary brake for most streetcars. It's not very efficient though; while cars have eight wheels, and brakes can be applied against all of them at once, their contact patch (where the wheel meets the rail) is tiny compared to a car's wheels.
Because of this most streetcars also employ track brakes. This is either a steel or wooden bar that can be installed between the wheels on the bogies or on the chassis itself that can be pressed into the track to provide additional friction. Those aren't applied by default; only when additional braking is needed. They can be used in an emergency braking situation or when traversing steep inclines (not a problem here, obv.). Based strictly on photos, it appears the trolleys from Portland do have track brakes, but I'm not sure that the W2 cars do.
Some cars also have a last-resort emergency brake called a wedge brake. If that's engaged the car drops a steel wedge between the wheels and the track. The pressure and friction of the car during a wedge-brake can actually weld the wedge to the track, so it's only used if absolutely needed. I don't know whether any of these cars have wedge brakes, though since the Portland cars are newer I'd think it's possible.
We don't know if that '70' at 15 mph' figure, assuming it's accurate, is against wheel braking only or if that factors in an available track braking.
Thirdly, does anyone know if the 70' stopping distance at 15 MPH includes reaction times? The National Association of City Transportation Officials have published a chart of braking and stopping distances for vehicles on their site. According to that, a vehicle travelling at 15 mph needs only 11' to stop, but factoring in response time increases that to 44'. 70' is worse, obviously, but if response time is factored in that's actually not horrible for a streetcar given the inherent braking deficiencies mentioned above.
*phew*. Hope at least some of you made it through all that.
-RBB
