Updated: Oct 4, 2022
Freeways are overly busy. everyone notices the congestion unless their head is buried in the sand, or their phone. there are simple things that can assist in navigating a little more stress free: lane drops. Believe it or not, there are lane markings indicating a lane is ending on interstate highways. The interstate and state highways are regulated by a not so simple book that is full of standards that are mandated by law. The manual on uniform traffic control devices, or mutcd for short is actually purchased by more lawyers than the cities, states and construction companies that apply & install the facilities combined. the book has significance & makes certain from Washington to new York, the signs and markings of the roads are all the same to help general public motor through safely.
when a lane is an exit only on a state route or major state highway, there's more to letting you know in advance than the lane veering off with an exit sign above. a physical gore point is a location where two lanes have separated and the pavement ends. coming up to a gore point, you have the paints lines on the road guiding drivers away from the gore point; this is called the theoretical gore, as illustrated in the figure above.
here's the nugget we're building up to: when a lane or lanes are an "exit only" off of a state route or free way, one half mile previous to the lane ending - you have a dotted white line. these dotted paint markings are double the normal thickness, i.e. 8-12" inches wide and start half a mile previous. on a four or six lane highway - that can really help make navigation a little more stress free.
this example by the convention center in Seattle, you have a 6 lane highway. the 3 lanes to the right are going to end up turning into i-90 east bound, this is illustrated by the wider paint markings in the #1 and #3 lanes from the right.
some states are more aggressive with their signing or markings, choosing to install optional guidance that makes travel less confusing for drivers. in this example, we have i-93 northbound in Henderson, Nevada. 2 lanes are going to exit but it's optional for the #2 lane from the right. posted speed limit is 65mph, motoring public's 85th percentile of speed is roughly 75-80mph.
these attributes are all accounted for to make roads safer and have less fatalities. not every driver has the same level of experience or knowledge regarding the signs and markings of the road, the standards of the mutcd are made to have consistency across the united states.