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Do I travel “up” or “down” to London from north of the city?
Except where there is obvious difference in elevation e.g. on a sloping road, how do native speakers decide whether to use up or down in phrases like up the road when referring to a location along the same road?
A very interesting question!
In the first place, there are no absolute rules - here in the UK, my wife and I sometimes disagree on which preposition sounds more natural in a given expression.
Secondly, the non-central senses of the prepositions (up connoting 'good', 'an improvement', or 'towards the central, main, important place' influence the choice. We often say 'going up town'; 'going up to university'. A connected association is between 'up' and 'in a generally north direction'.
It is not so much that there are no rules, more that there are a few of them that contradict. It really depends where you are and what road you are talking about.
If you are in the middle of nowhere on an open road, 'up the road' is your direction of travel - the village is a few miles up the road.
If you are sat a home discussing the trip, you go 'up north' or 'down south', as shown on a map.
but...
strictly speaking you go up to the capital city, so someone who lives up north, should go up to London even though it is down south.
In a city, you go 'down the road' if the building numbers are getting smaller, which usually means you are going towards the centre, or 'down town'. This still applies even if you are already that way and 'down town' is also 'up the road', or would be if you weren't in a city.
In practical use, the whole thing is very fuzzy, so it is hard to get it so wrong that people notice.
I think the short answer is that there's no real rules about "up the road" versus "down the road". They mean essentially the same thing.
For what it's worth: When I lived near New York City, the streets there are mostly numbered: First Avenue, Second Avenue, etc, so "downtown" meant toward lower-numbered streets and "uptown" meant toward higher-numbered streets. Everywhere I've lived in the U.S. "downtown" refers to the business district of a city. But other than New York, I've never heard a part of a city referred to as "uptown". I've also never heard that carried over to say that "down the street" means toward the business district and "up the street" means away from the business district or any such thing.
I've also never heard anyone say that "up the road" means travelling in the direction that goes uphill.
Possibly related: When talking about a river or stream, "downstream" means the direction that the water is flowing, and "upstream" means the opposite direction. So if you say, "That town is upstream from here", you mean that it is along the river but in the opposite direction from the way the water flows. As water generally flows downward, this makes sense. (There's an old riddle: The five largest rivers in the world all flow in the same direction. What direction is that? Answer: Downhill.)
In American English, I do not think that there is any semantic difference between up and down in the phrases when used to discuss geography.
However, the phrase down the road is regularly used to mean in the future
if an event is a particular period of time down the road, it will not happen until that period has passed This is a wonderful invention, but a marketable product is several years down the road yet.
(American) if you say that something will happen down the road, you mean it will happen in the future We may at some point buy a house but that's down the road.
The phrase up the road is not regularly used in this manner.
This idiomatic use may help explain the incidence differences between the phrases:
