Interestingly, I demoed and shipped a wayfinding solution for a mobile app earlier this year, where I just brute forced the shortest paths between all pairs ~200 "intersections" in the area of interest for this event, and just stored the answers in a KV store based on the intersections (then does some cheesy last 20m stuff to route you to and from the nearest intersections to your location and destination).
In a limited-enough space (like an event), this works out just fine. I'm glad I'm not the guy who needs to solve GoogleMap's routing problems though. I wonder if they have a huge BigTable store of every street intersection pair on the planet and a recalculated best route between them? I _hope_ they do something smarter than my "works in my constrained requirements space" brute-force hack...
Route-finding is much simpler than traveling salesperson.
The hard part for real-world directions is getting the cost-function right. Older map systems used to make some very questionable assumptions that made them quite inaccurate (one example; assume all highway miles are equal; some were 55MPH and have traffic lights, railroad crossings and stop-signs others were 65 with no at-grade intersections -- today even higher speed limits are seen as the lingering effects of the national speed-limit have worn off).
We have a related problem in the UK. Sometimes very small "country lanes" have no explicit speed limit, so defaults to national speed limit of 60mph, which you would have to be suicidal to drive at (or just hate your car), but Google maps still often route finds along these roads.
This. Google has a major advantage in that they have a massive dataset. They can use their data to improve the cost function even in real time to detect traffic.
Up until around 1990 or so 55MPH was the maximum speed limit; this was originally to conserve fuel. Up until 1995 55MPH was the maximum except for roads very far from population centers.
Even after 1995, many states were very slow to raise the speed limit (I lived near the Maryland/Virginia boarder and remember Maryland did well before Virginia), and when they did raise the speed limit it was by small amounts.
Today, you can drive from Los Angeles to New York and not hit any significant stretches of freeway with speedlimits under 65, and west of the Mississipi river, you will spend most of it at 70mph or higher.
On top of that, the actual speed that will get you pulled over can be much higher (In CA you are very unlikely to get pulled over for single-digit MPH speeding on a freeway, making a 65 speed limit a de-facto 74; in the northeast US it's not uncommon to get pulled over for going just 5MPH over the posted limit).
> Up until around 1990 or so 55MPH was the maximum speed limit
The NMSL (National Maximum Speed Limit) was enacted in 1973, modified in 1987 to allow 65 mph speed limits on rural interstates, and repealed in 1995.
Many states in the southeast, midwest and west raised their posted speed limits very soon after the NMSL was repealed. States in the northeast took a bit longer to update their laws to remove their state maximum speed limit.
Edit: to add value to the conversation: in germany I find googles estimates on long car trips quite accurate. And I'm actually a very erratic driver, sometimes taking every hole in traffic I can to get ahead, just slowing down to speed limit+20km/h where there is a speed trap, sometimes just cruising 80km/h on open autobahn getting overtaken by cargo trucks
FWIW, Advisory speed-limits on autobahn are similar to the western US statutory speed limits (130km/h == 80mi/h). That being said, 200km/h and no other moving violations would quite possibly get you thrown in jail in "The land of the free"
When my local public transport (bus+train) did a major-ish route overhaul, routing directions on Maps glitched out for a couple days and showed large "black spots" (maybe 5-15mi in size?) where regions of generally accurate/useful routing were slapstuck together with large straight lines that cut diagonally through backyards, houses, major highways, etc (and sadly didn't account for runway room so weren't even flyable). So in a scenario where you were zoomed out enough to see 2-3 towns, you'd get a complex route shape in one part of the map, another complex route shape in another part of the map, then one single "nope I can't do this" giant line connecting the two regions. The giant line often connected to the complex shapes at awkward angles, eg 60-70°.
Unfortunately IIRC most of the screenshots I took show my actual address/immediate surrounding area etc, so they'd be fairly heavily censored. If anyone [is actually reading this and] is especially interested, I can try braving my scary not-organized screenshot archive and try and find them.
