上下線

Two questions.
1. How do you normally translate 上下線? I usually use something awkward like both directions or both sides of the road. Or if I know the road, I'll say eastbound/westbound or southbound/northbound.
2. How do you determine the actual directions? I know usually 上 is towards a city and 下 is away. But what if you are in inaka somewhere with no clear big city. Is it defined by where the road itself started? Local custom?

一方、名神の天王山・梶原トンネルの場合は、東名や中央よりもさらに交通量が多く、ほぼ毎日渋滞が発生していたため、北側に新設された上り線も4車線とされた。ここはほぼ直線部で、平野部に突き出た天王山（羽柴秀吉と明智光秀の決戦が行われた地）をトンネルで貫いている形なので、上下線がほぼ並行している。

4車線のトンネルは、直径が大きくなりすぎて不経済なため、新たなトンネル部も2車線＋2車線に分離して建設された。その結果、上下線ともに左ルートと右ルートに分かれることになったのである。

この天王山・梶原トンネル付近は、合計8車線が並行して走り、上下線がそれぞれ左右に分離するので、日本の高速道路の中では最も壮観だ。こちらの完成は1998年。世紀を挟んで、これら4区間が次々と完成したが、若い層はそれ以前を知らないため、「なぜ左右に分かれてるの？」と思うのも当然だろう。

2)
上 indicates the direction towards Tokyo, and 下 is away from Tokyo in your example case.

And in the case of train lines I would translate 上下線 as inbound/outbound lines (although depending on the context there may be a better translation).

Toritoribe said:

2)
上 indicates the direction towards Tokyo, and 下 is away from Tokyo in your example case.

Click to expand...

Thanks. I'm asking about the general case. I only posted that article as an example of usage of the word.

Here's a general example which doesn't have context because it's not road-specific:

上下線で誤差が大きい場所については、接合を実施

I guess there's really nothing this succinct in English.

When the term 上下線 is used for a road, not 左右両車線 or something, it always implies that the directions toward and away from Tokyo, a near big city or the central part of a city in the context even if it's not clearly mentioned in the manual/explanation.

Toritoribe said:

When the term 上下線 is used for a road, not 左右両車線 or something, it always implies that the directions toward and away from Tokyo, a near big city or the central part of a city in the context even if it's not clearly mentioned in the manual/explanation.

Click to expand...

How about a road like Route 45 here?
It connects Sendai and Hachinohe. Sendai direction is 上?
Or Route 4 here? It goes to Morioka, then Sendai so maybe that way is 上?
Or Route 9 here. Towards Tottori is 上?

The basic idea is that toward the starting point of a route is 上り, and to the end point is 下り. Tokyo or big cities are often the starting point of major routes, so the directions toward these places are often 上り.

Since the directions 上り and 下り are used throughout each route, it's not changed between the north side and south side or east side and west side of a big city on the route. For example, the starting point of Route 4 is Tokyo and the end point is Aomori, so, toward Tokyo is always 上り. Thus, at a place on the south side of Sendai, away from Sendai is 上り even if the place is very close to Sendai and 上り looks like away from a big city Sendai and toward to a rural area.

Route 45 is from Sendai to Hachinohe, and Route 9 is from Kyoto to Shimonoseki. It's clear which is which for your rest two examples, isn't it?

However, there seems to be exceptions. Although the starting point of Route 122 is Nikko and the end point is Tokyo,
toward Tokyo is called 上り in road traffic information (probably because it's confusing).

道路交通情報では、終点である東京へ向かう方向を上りと表現している

That's helpful, thank you.