Its not just about the slippery surface though, imagine one being used to power traffic lights, because they are longer than the wheelbase on most bikes, you could be stopped at lights maybe half on the front of one of these things, so your back wheel or maybe even your whole bike is on plate, and a car approaches behind and hits the ramp. Because the car is heavier than you are, it will make the bike jerk upwards and if you are vertically challenged, you could be in a spot of bother. Now, the more experienced of us would pull further forward/hold back and wait for room, rather than stop half on/half off the ramp, but those with little experience could find themselves loosing balance. Also, the way it moves as you ride over it in any conditions is bound to cause some problems, your front end dropping as the front wheel hits the ramp and then rising as your rear wheel hits it.
LOVE IS GIVING SOMEONE THE ABILITY TO DESTROY YOU, THEN TRUSTING THEM NOT TO.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, But rather to skid in sideways, chocolate in one hand, VODKA in the other, body thoroughly used up, totally worn out and screaming…….WOO HOO, WHAT A RIDE!!