Highways in Canada

[Dado]

Originally Posted by go_leafs_go02

I like A4 better than B4 because it first of all doesn't seem as dangerous as vehicles flying off the freeway don't enter a large loop where they can tip over.

Seems like a safety feature to me: it forces drivers to actually SLOW DOWN when exiting the freeway because the consequences of not doing so are so high to themselves. That would apply most to the B2 of course which completely eliminates any possibility of a high speed offramp.

The loop ramps in an A4 come from a lower speed road or highway.

The loop ramps are the worst aspect of the design.

The second thing is that a B4 requires left turns off a major roadway, in which some major signal timing changes are needed or queues will back up across the bridge structure and through the other signal on the other side of the interchange.

What a tragedy.

I wish BC would use more A4 interchanges, they've just introduced one at Highway 1 and 176 Street that works fantastically, and I hope to see additional introduction in the future.

I wonder if this cyclist here will agree with you when he has to cross the traffic entering the loop ramp...

Count yourselves lucky that BC doesn't use more of them. I sure wish Ontario wouldn't but unfortunately for us the MTO has a love affair with this bad interchange design - the entire province is littered with the things.

They're a menace to pedestrians and cyclists, which in this day and age ought to be enough to remove them from contention outright, but then the MTO has never really cared for any kind of transport besides cars and trucks.

Besides that, they're illogical (turn right to turn left?), they clog up the right hand lane with would-be freeway traffic ahead of the interchange where it gets to mix it up with cyclists and buses, they're wasteful of land and require longer spans over the freeway than diamonds, the average driver can't use the loop ramps worth a damn to accelerate in lanes which are artificially short due to presence of the second onramp, they require a ridiculous amount of effort to clear the ramps of snow in the winter (think about the route snow plows have to take to clear all six ramps compared to a diamond) and buses using the freeway can't make use of them in an unmodified state for a bus stop like they can with a diamond.


Overall, the A4 Parclo is the worst standard interchange design in existence after the full cloverleaf. Even the A2 is better since the loop ramp is usually tied into an intersection forcing cars to make a proper slow speed right turn onto it and it will have a longer acceleration lane on the freeway itself (since the other onramp doesn't exist) so even if you have the misfortune to be stuck behind someone who can't accelerate on a curve at least you have a reasonable chance of being able to get up to speed on the rest of the merge lane.

I just cannot fathom why highway engineers in general and those of the MTO in particular are so infatuated with this horrible interchange design.

The best is probably the diamond, with the B2 being a respectable second.