This script makes the origin and destination fields on the NJ Transit train schedule page persistent.

njt_tssp.user.js

// ==UserScript==
// @name         NJ Transit Train Schedule Station Persister
// @namespace    https://www.wecsam.com/
// @version      0.1
// @description  This script fills the origin and destination fields with the last values that you entered.
// @author       You
// @match        https://www.njtransit.com/sf/sf_servlet.srv?hdnPageAction=TrainTo
// @match        https://www.njtransit.com/sf/sf_servlet.srv?hdnPageAction=TrainTo#
// @grant        none
// ==/UserScript==

(function() {
	'use strict';
	var elForm = document["frm_tr_schedules"],
		elSelOrigin = elForm["selOrigin"],
		elSelDestination = elForm["selDestination"],
		/**
		 * This function finds the <option> element inside the given <select>
		 * element that matches the given value and then selects that <option>.
		 *
		 * @return true if a matching <option> was found, false otherwise
		 */
		setSelectElementValue = function(elSelect, value){
			var i;
			for(i = 0; i < elSelect.children.length; ++i){
				if(elSelect.children[i].value == value){
					elSelect.children[i].selected = true;
					return true;
				}
			}
			return false;
		},
		makeSelectElementPersistent = function(elSelect, localStorageKey){
			// First, load the last value.
			if(localStorage.hasOwnProperty(localStorageKey)){
				setSelectElementValue(elSelect, localStorage[localStorageKey]);
			}
			// Add an event listener to save changes.
			elSelect.addEventListener("change", function(event){
				localStorage[localStorageKey] = elSelect.value;
			});
		};
	// Make the <select> elements persistent.
	makeSelectElementPersistent(elSelOrigin, "trainToSelOrigin");
	makeSelectElementPersistent(elSelDestination, "trainToSelDestination");
	// Add a reverse button.
	var elBtnReverse = document.createElement("input");
	elBtnReverse.type = "button";
	elBtnReverse.value = "Reverse Trip";
	elBtnReverse.addEventListener("click", function(event){
		var old = elSelOrigin.value;
		setSelectElementValue(elSelOrigin, elSelDestination.value);
		setSelectElementValue(elSelDestination, old);
	});
	elForm.querySelector("input[type=submit]").parentElement.appendChild(
		elBtnReverse
	);
})();