1) "Posted speed (prevailing…

1) "Posted speed (prevailing) should be 20 km/h lower than the design speed."

This policy is the one most important cause of speeding in Ontario. Drivers feel that the roadway can be safely driven faster than allowed, and so they do.

The many examples in southern Ontario of posted speeds less than 20 km/h below the design speed (three of them on provincial highways) show that posting a more appropriate speed limit does not result in faster driving, but only legalizes existing safe speeds.

The 2+1 sites should generally be posted at 10 km/h below design speed from the beginning, as 2+1 is already a safety upgrade over the current undivided design, provided that slow vehicles are properly taken care of (see below).

2) "No Adjacent Vehicles (Agricultural or Horse Drawn Vehicles)"

While the selected sites are said to be free of slow vehicles, the design must still take them into account, as there are no alternative routes for a slow vehicle to use. I'm thinking less of tractors or horses, and more of bicycles and limited-speed motorcycles.

On an undivided highway, these can be passed with ease, as their low speed shortens the time spent in the opposite lane. On a 2+1 highway, the long barrier-protected single-lane sections would tempt drivers to pass at an unsafe distance.

To ensure safety, the single-lane side should have pavement wide enough to pass a slow two-wheeled vehicle at speed (perhaps 5 m from barrier to edge of pavement). Where the right-of-way doesn't allow for this, fast vehicles must be able to brake in time when approaching a slow vehicle: there must be signs warning about the end of the paved shoulder, and depending on sightlines, lower speed limits may be needed.