pgrouting - Choosing an algorithm with a predominance for a specific type of road

Question

I would like to use one of pgrouting's algorithm to find the (shortest) path between 2 points with: (a) predominance for a specific type of road and (b) intemediate points.

To build the data I used the osm2pgrouting. I would like to focus first on the issue (a).

1. Is there an algorithm where I could define my preferences for the road type (in table ways class_id column class_id which represents road type or in table osm_way_types)?
2. If not how should I tweak my database? Knowing that I used the osm2pgrouting --> there is table public.osm_way_classes there is max_speed but it seems poor choice for tweaking it. I would like to leave it alone. I didn't really find anything useful in other tables. Any ideas?

Problem (b) (LESS IMPORTANT) is to determine if the length of searched path is less than for example 10km. If no then path should visit one of specified intermediate point (or points).
I don't think there are algorithms in pgrouting which condider these "stops" (intermediate points between source and target). I think this problem (b) should be solved by searching path from point1 to point2 and then from p2 to p3 etc. etc. but I don't know yet how to determine those points.

Answer 1

Graph theory in general solves shortest path based on edge weights. IE: to get from A to B in the graph it will select those edges that minimize sum of the weights of the edges in the path. So in pgRouting you select the weights as the edge lengths of shortest path length, or can compute the weight as the time to traverse the edge time = length/speed, for shortest time, but for you problem you can make your own weights with an equation like length*preference where preference is some fraction where smaller is more preferred. Obviously you will get back cost based on this factor along with the edge ids and a simple join useing the edge id will get you bcak to the original table. This strategy should work for most any of our algorithms.