H’way 1 between somewhere N of Khao Phra Ngam (N14.91699 E100.60584) and E of Takhli (N15.27146 E100.36551) is a single lane country h’way. I propose that we downgrade this section to “Primary” to reflect this, the classification scheme in the wiki notwithstanding.
According to Key:highway the highway tag describes “the importance of the highway for the road grid” which “gives the user of a highway more useful information than … physical characeristics”. This fits exactly to this situation. Highway 1 is the connection from Bangkok through the northern part of Thailand to Birma. It should be shown on a map in the same style everywhere to be easily spotted. In all other maps I’ve seen the style of highway 1 doesn’t change.
Therefore highway 1 as well as the highways 2, 3 and 4 should be highway=trunk all over.
I have no problem with the definition of the tag, but please take another look at the map: h’way 1 S of the junction with 32 starts to meander. It is neither the shortest nor the fastest or biggest route between Bkk and the North. Maybe it was when it was first built. That role now goes to the 32. Even if you wanted to take the 11 to Uttaradit you wouldn’t make the loop through Saraburi; you would take the 32. I think we shouldn’t stick to definitions rigidly, but be a little flexible.
I’m looking at the ESRI GPS map here and both 32 and 11 are trunk roads. Yes, they made the 1 loop a trunk, too.
That’s a different animal: Showing the new highway no. 32 as a shortcut to the old highway no. 1 between Uthai Thani and Bang Pa-In by upgrading the 32 to trunk. This map section shows that this has be done already. When I remember correctly this is in accordance with the traffic signs. Coming from Nakhon Sawan and heading to Bangkok the signs are leading to highway 32.
But downgrading this section of highway no. 1 as proposed is in my opinion no good idea. It’s confusing when the style of the highway changes on its course, i.e. in Mapnik between green and red line. The importance of this part might be still the same for drivers who don’t come from Bangkok but from this area or from highway no. 2 heading north at Saraburi and not wanting to go via Bang Pa-In. And finally to my knowledge the Department of Highways did not downgrade no. 1. Do foreigners know it better?
Compare it with highway no. 4. It’s classified as trunk along its whole course (green line in Mapnik). But in the mountains there’s no separation and it’s partially less than 6 meters wide. And that’s just what the Wiki says: road grid not physical characteristic makes the difference.