Symbolism, Imagery, Allegory
Bram Stoker, as you've probably noticed, is totally obsessed with trains.
In the world of Dracula, trains are representative of Stoker's wider interest in the latest, most up-to-date technology. It's hard for modern readers to remember, but all the technologies mentioned in Dracula—Seward's phonograph, the telegrams, the trains, the blood transfusions, Mina's typewriter and even her shorthand—were super high-tech in 1897.
If Stoker were writing today, the technologies would obviously be different. Instead of recording his journal entries on a phonograph (an early recording device), Dr. Seward would blog about his patients. Instead of sending a telegraph to warn the men that Dracula was on the move, Mina would live-tweet.
Why does Stoker include all these details to show how up-to-date and high-tech his characters are? Well, one effect is to create a contrast between the science and technology Van Helsing and his crew have on their side with the tradition and superstition governing the world of Dracula.
But even though the good guys in Dracula are able to use technology to their advantage in many cases, it has its limits: The blood transfusions don't save Lucy's life, and a blip in the telegraph system keeps Seward from getting Van Helsing's message in time rush to Lucy's aid. Technology and science, it seems, don't have all the answers.
In fact, Van Helsing, Seward, and the others actually have to get over their faith in science, logic, and modern technology in order to defeat Dracula. They have to accept, first of all, that vampires exist, and they have to re-educate themselves, learning ancient traditions and superstitions, to figure out how to kill a vampire. The Winchester rifles that Quincey Morris brings are great against the Szgany in the final fight scene, but killing Dracula requires something more primitive—a big knife and a stake through the heart.