I never knew trains were so long...

[Shoestring]

Longest I've ever ridden was from Ipswitch, South Dakota to Aberdeen, South Dakota with 430 grain cars! Ipswitch to Aberdeen is like only 35 miles and I was in the rear unit when we picked up the last set of add-ons. The reason I knew how long it was is because the brakeman came back and told me what we were doing was going ahead (while out), plus being that close to the Aberdeen yards,... that we were taking all the grainers into the yard and saving the GP-38's a trip out to Ipswitch the next day. We still only had three units at around 3,200 HP each, but slowly made it on in to Aberdeen.
(This also was when Burlington Northern in that area was running "Dark Territory" back in 1991)........................The longest set of trailing units on a train I rode was 21 units. They were doing a "unit transfer" from Marysville, Kansas to Kansas City's "Neff Yards".

Longest US Freight:

"The longest and heaviest freight train on record was
one about 4 miles in length consisting of 500 coal cars with three 3600
hp diesels pulling and three more in the middle, on the Iaegar, WV, to
Portsmouth, OH stretch of 157 miles on the Norfolk & Western RR on Nov
15, 1967. The total weight was nearly 47,250 tons."

Longest Freight Ever:

"The heaviest and longest train, with the largest number of wagons
recorded, was run on the 3'6" gauge Sishen-Saldanha railway in South
Africa on 26-27 August 1989. The train consisted of 660 wagons each
loaded to 105 tons gross, a tank car and a caboose (guards van). The
train was moved by nine 50kv electric and seven diesel electric
locomotives distributed along the train. The train was 7.3km
(4.5miles) long and weighed 69393 tons, excluding locomotives. It
travelled 861km (535 miles)."

I also read it took somewhere around 4 miles to stop the train.

In making this post I found the apparent record breaker:

"The longest train ever was 7.353 km (4.568 miles) long, and consisted of 682 ore cars pushed by 8 powerful diesel-electric locomotives. Assembled by BHP Iron Ore, the train travelled 275 km (171 miles) from the company's Newman and Yandi mines to Port Hedland, Western Australia, on June 21st, 2001."

also:

"While not having set a world record for length, there's a train line in the Sub-Sahara that is used to transport copper from mines deep inland to harbors, where it is loaded onto ships, and those trains are regularly more than 2.5 miles long, and that as said on a regular basis, and not just on a one-off occasion."

So yeah, trains can be real damned long.