diff --git a/backend/src/graph.rs b/backend/src/graph.rs
index 2f5beca..4f6f74d 100644
--- a/backend/src/graph.rs
+++ b/backend/src/graph.rs
@@ -43,6 +43,7 @@ pub enum Direction {
     None,
 }
 
+// TODO Justify why PublicTransit isn't captured here
 #[derive(Clone, Copy, Enum, Debug, Serialize, Deserialize)]
 pub enum Mode {
     Car,
diff --git a/backend/src/isochrone.rs b/backend/src/isochrone.rs
index 07151a1..ddfd79f 100644
--- a/backend/src/isochrone.rs
+++ b/backend/src/isochrone.rs
@@ -2,6 +2,7 @@ use std::collections::{BinaryHeap, HashMap, HashSet};
 use std::time::Duration;
 
 use anyhow::Result;
+use chrono::NaiveTime;
 use geo::{Coord, Densify};
 use utils::{Grid, PriorityQueueItem};
 
@@ -14,13 +15,14 @@ pub fn calculate(
     req: Coord,
     mode: Mode,
     contours: bool,
+    public_transit: bool,
     mut timer: Timer,
 ) -> Result<String> {
     // 15 minutes
     let limit = Duration::from_secs(15 * 60);
 
     timer.step("get_costs");
-    let cost_per_road = get_costs(graph, req, mode, limit);
+    let cost_per_road = get_costs(graph, req, mode, public_transit, limit);
     timer.push("render to GJ");
 
     // Show cost per road
@@ -51,7 +53,17 @@ pub fn calculate(
     Ok(x)
 }
 
-fn get_costs(graph: &Graph, req: Coord, mode: Mode, limit: Duration) -> HashMap<RoadID, Duration> {
+fn get_costs(
+    graph: &Graph,
+    req: Coord,
+    mode: Mode,
+    public_transit: bool,
+    limit: Duration,
+) -> HashMap<RoadID, Duration> {
+    // TODO plumb in
+    let start_time = NaiveTime::from_hms_opt(7, 0, 0).unwrap();
+    let end_time = start_time + limit;
+
     let start = graph.closest_intersection[mode]
         .nearest_neighbor(&[req.x, req.y])
         .unwrap()
@@ -59,23 +71,25 @@ fn get_costs(graph: &Graph, req: Coord, mode: Mode, limit: Duration) -> HashMap<
 
     let mut visited: HashSet<IntersectionID> = HashSet::new();
     let mut cost_per_road: HashMap<RoadID, Duration> = HashMap::new();
-    let mut queue: BinaryHeap<PriorityQueueItem<Duration, IntersectionID>> = BinaryHeap::new();
+    let mut queue: BinaryHeap<PriorityQueueItem<NaiveTime, IntersectionID>> = BinaryHeap::new();
 
-    queue.push(PriorityQueueItem::new(Duration::ZERO, start));
+    queue.push(PriorityQueueItem::new(start_time, start));
 
     while let Some(current) = queue.pop() {
         if visited.contains(&current.value) {
             continue;
         }
         visited.insert(current.value);
-        if current.cost > limit {
+        if current.cost > end_time {
             continue;
         }
 
         for r in &graph.intersections[current.value.0].roads {
             let road = &graph.roads[r.0];
             let total_cost = current.cost + cost(road, mode);
-            cost_per_road.entry(*r).or_insert(total_cost);
+            cost_per_road
+                .entry(*r)
+                .or_insert((total_cost - start_time).to_std().unwrap());
 
             if road.src_i == current.value && road.allows_forwards(mode) {
                 queue.push(PriorityQueueItem::new(total_cost, road.dst_i));
@@ -83,6 +97,23 @@ fn get_costs(graph: &Graph, req: Coord, mode: Mode, limit: Duration) -> HashMap<
             if road.dst_i == current.value && road.allows_backwards(mode) {
                 queue.push(PriorityQueueItem::new(total_cost, road.src_i));
             }
+
+            if public_transit {
+                for stop1 in &road.stops {
+                    // Find all trips leaving from this step before the end_time
+                    for next_step in graph.gtfs.trips_from(
+                        *stop1,
+                        current.cost,
+                        (end_time - current.cost).to_std().unwrap(),
+                    ) {
+                        // TODO Awkwardly, arrive at both intersections for the next stop's road
+                        let stop2_road = &graph.roads[graph.gtfs.stops[next_step.stop2.0].road.0];
+                        for i in [stop2_road.src_i, stop2_road.dst_i] {
+                            queue.push(PriorityQueueItem::new(next_step.time2, i));
+                        }
+                    }
+                }
+            }
         }
     }
 
diff --git a/backend/src/lib.rs b/backend/src/lib.rs
index 6c52637..79191ee 100644
--- a/backend/src/lib.rs
+++ b/backend/src/lib.rs
@@ -84,7 +84,7 @@ impl MapModel {
             "car" => Mode::Car,
             "bicycle" => Mode::Bicycle,
             "foot" => Mode::Foot,
-            // TODO Unimplemented
+            // Plumbed separately
             "transit" => Mode::Foot,
             // TODO error plumbing
             x => panic!("bad input {x}"),
@@ -94,6 +94,7 @@ impl MapModel {
             start,
             mode,
             req.contours,
+            req.mode == "transit",
             Timer::new("isochrone request", None),
         )
         .map_err(err_to_js)