There are things we do in BusBoss to minimize left turns, but we do not prevent them. Specifically, in the routing algorithm, we assign a "value" for navigating an intersection. It's not exactly like this, but it's close enough for discussion purposes.
BusBoss uses turn penalties and road classifications to do this right.
There are many factors to consider when routing vehicles. More important than turn penalties, BusBoss prefers higher classifications of roads. While most stops are on local roads, BusBoss will attempt to travel on county roads instead. During inclement weather, county roads are likely to get more attention from snow plows, which makes them safer. Additionally, higher classifications of roads tend to have wider shoulders, also making them safer. We do not have access to information regarding snow plow routes or shoulder widths, so we base these decisions on assumptions that higher
class roads are better maintained. This may not be true for particular roads, but I believe it to be "generally" true.
Most bus stops are on local roads which is certainly better (generically speaking) because local roads have less traffic and are therefore safer for students to wait at a bus stop. When I mentioned earlier that BusBoss prefers higher classifications of roads, this will mostly be noticed in long stretches of the route without any stops. For example, the first path and/or last path on a route are usually the longest (distance between stops). This is where you would notice BusBoss preferring higher classes of roads and the turn penalties have more of an influence.
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