I'm using the food/garbage and fence add-ons.
As I understand the term, the key features that make something a highway are, in simutrans terms:
- No crossings at grade
- No on-track stops
- No 90-degree turns
- Having two one-way roads, so fast cars can overtake smaller ones
- Being protected from conversion to city roads, either by distance from a city, by being a tunnel or an elevated way, or by a fence
- Having a minimum speed limit
Other definitions are possible, but I'm mainly interested in discussing things that meet this definition.
The minimum speed limit sign has intro_year = 1930, which struck me as rather early for a minimum speed limit of 80 km/hr. I did some checking, and in 1930, road tunnels are the only road type that will allow speeds that high, and they have a maximum speed of 80 km/hr. Therefore, there will be no overtaking. The minimum speed limit sign might be useful to keep your tunnels uncongested, but that doesn't really count as a highway to me.
In 1940, Asphalt roads become available, allowing speeds up to 110 km/hr. At that time, the only convoys capable of reaching 80 km/hr are the H-Trans Car Carrier, the H-Trans Car-Carrier plus any trailer it can be attached to, and the Milk Truck. Several of those have speeds greater than 80, so overtaking can occur.
I checked operational profitability: revenue - operating expenses, per unit. If my calculations are correct:
- The most profitable way to carry Cars by road at that time is the Car Carrier, w/o the corresponding trailer.
- There are three goods that can be carried more profitably on the highway using an empty Car Carrier truck to pull them, than by being pulled by a slower truck carrying the same good type:
- If you're lucky enough, you may be able to find a route where you can carry both Cars and some other good. On such a route, a Car Carrier truck + other good trailer can be more profitable than carrying the Cars and the other goods separately. There's only two goods that can be carried that way where it isn't more profitable:
The thing that bothers me about this is that I can't remember ever seeing a real-world combination of a Car Carrier truck (full or empty) and a trailer carrying any other good. Now, the remarks I made above about them being more profitable cease to be true by the mid 1960s, when fast trucks carrying oil, bulk goods, garbage, cooled goods, and lumber became available. I wasn't born till 1958, so I probably wouldn't have noticed - but were there ever actually convoys like those?
If not, then something should probably be done to make them either unavailable or unprofitable. If so, the minimum speed limit sign wouldn't really come into it's own until the early 60's, which seems reasonable to me.