diff --git a/debug_initialmap/src/main.rs b/debug_initialmap/src/main.rs
index 268f840450..1bc928945b 100644
--- a/debug_initialmap/src/main.rs
+++ b/debug_initialmap/src/main.rs
@@ -1,14 +1,17 @@
 use abstutil::{find_next_file, find_prev_file, read_binary, Timer};
 use ezgui::{Color, EventCtx, EventLoopMode, GfxCtx, Key, Text, GUI};
 use geom::{Distance, Polygon};
-use map_model::raw_data;
-use map_model::raw_data::{StableIntersectionID, StableRoadID};
+use map_model::raw_data::{StableIntersectionID, StableRoadID, InitialMap};
 use std::collections::HashSet;
 use std::{env, process};
 use viewer::World;
 
+// Bit bigger than buses
+const MIN_ROAD_LENGTH: Distance = Distance::const_meters(13.0);
+
 struct UI {
     world: World<ID>,
+    data: InitialMap,
     filename: String,
     // TODO Or, if these are common things, the World could also hold this state.
     selected: Option<ID>,
@@ -17,9 +20,13 @@ struct UI {
 }
 
 impl UI {
-    fn new(filename: &str, world: World<ID>) -> UI {
+    fn new(filename: &str, ctx: &mut EventCtx) -> UI {
+        let data: InitialMap =
+            read_binary(filename, &mut Timer::new("load InitialMap")).unwrap();
+        let world = initial_map_to_world(&data, ctx);
         UI {
             world,
+            data,
             filename: filename.to_string(),
             selected: None,
             hide: HashSet::new(),
@@ -28,7 +35,9 @@ impl UI {
     }
 
     fn load_different(&mut self, filename: String, ctx: &mut EventCtx) {
-        self.world = load_initial_map(&filename, ctx);
+        let data: InitialMap =
+            read_binary(&filename, &mut Timer::new("load InitialMap")).unwrap();
+        self.world = initial_map_to_world(&data, ctx);
         self.selected = None;
         self.filename = filename;
         self.hide.clear();
@@ -64,6 +73,13 @@ impl GUI for UI {
                 self.selected = None;
             }
         }
+        if let Some(ID::HalfRoad(r, _)) = self.selected {
+            if ctx.input.key_pressed(Key::M, "merge") {
+                self.data.merge(r);
+                self.world = initial_map_to_world(&self.data, ctx);
+                self.selected = None;
+            }
+        }
         if !self.hide.is_empty() {
             if ctx.input.key_pressed(Key::K, "unhide everything") {
                 self.hide.clear();
@@ -92,7 +108,7 @@ fn main() {
     let args: Vec<String> = env::args().collect();
     ezgui::run("InitialMap debugger", 1024.0, 768.0, |ctx| {
         ctx.canvas.cam_zoom = 4.0;
-        UI::new(&args[1], load_initial_map(&args[1], ctx))
+        UI::new(&args[1], ctx)
     });
 }
 
@@ -112,13 +128,11 @@ impl viewer::ObjectID for ID {
     }
 }
 
-fn load_initial_map(filename: &str, ctx: &mut EventCtx) -> World<ID> {
-    let data: raw_data::InitialMap =
-        read_binary(filename, &mut Timer::new("load InitialMap")).unwrap();
-
+fn initial_map_to_world(data: &InitialMap, ctx: &mut EventCtx) -> World<ID> {
     let mut w = World::new(&data.bounds);
 
     for r in data.roads.values() {
+        let len = r.trimmed_center_pts.length();
         if r.fwd_width > Distance::ZERO {
             w.add_obj(
                 ctx.prerender,
@@ -127,12 +141,12 @@ fn load_initial_map(filename: &str, ctx: &mut EventCtx) -> World<ID> {
                     .shift_right(r.fwd_width / 2.0)
                     .unwrap()
                     .make_polygons(r.fwd_width),
-                Color::grey(0.8),
-                Text::from_line(format!(
-                    "{} forwards, {} long",
-                    r.id,
-                    r.trimmed_center_pts.length()
-                )),
+                if len < MIN_ROAD_LENGTH {
+                    Color::CYAN
+                } else {
+                    Color::grey(0.8)
+                },
+                Text::from_line(format!("{} forwards, {} long", r.id, len)),
             );
         }
         if r.back_width > Distance::ZERO {
@@ -143,12 +157,12 @@ fn load_initial_map(filename: &str, ctx: &mut EventCtx) -> World<ID> {
                     .shift_left(r.back_width / 2.0)
                     .unwrap()
                     .make_polygons(r.back_width),
-                Color::grey(0.6),
-                Text::from_line(format!(
-                    "{} backwards, {} long",
-                    r.id,
-                    r.trimmed_center_pts.length()
-                )),
+                if len < MIN_ROAD_LENGTH {
+                    Color::GREEN
+                } else {
+                    Color::grey(0.6)
+                },
+                Text::from_line(format!("{} backwards, {} long", r.id, len)),
             );
         }
     }
diff --git a/map_model/src/make/initial/merge.rs b/map_model/src/make/initial/merge.rs
index dd1410dc6c..0ba559c052 100644
--- a/map_model/src/make/initial/merge.rs
+++ b/map_model/src/make/initial/merge.rs
@@ -56,7 +56,7 @@ pub fn short_roads(map: &mut InitialMap, timer: &mut Timer) {
 }
 
 // Returns the retained intersection.
-fn merge(
+pub fn merge(
     map: &mut InitialMap,
     merge_road: StableRoadID,
     timer: &mut Timer,
diff --git a/map_model/src/make/initial/mod.rs b/map_model/src/make/initial/mod.rs
index b588652d3a..7e55cb1db3 100644
--- a/map_model/src/make/initial/mod.rs
+++ b/map_model/src/make/initial/mod.rs
@@ -163,4 +163,11 @@ impl InitialMap {
         abstutil::write_binary(&path, self).expect(&format!("Saving {} failed", path));
         println!("Saved {}", path);
     }
+
+    pub fn merge(
+        &mut self,
+        r: StableRoadID,
+    ) {
+        merge::merge(self, r, &mut Timer::throwaway());
+    }
 }