diff --git a/.gitignore b/.gitignore
index 3ca43ae..53fd210 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
+# Custom
+assets/
+
 # ---> Rust
 # Generated by Cargo
 # will have compiled files and executables
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..8961b00
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "metroviz"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bevy = { version = "0.11.0", features = ["dynamic_linking"] }
+rand = "0.8"
+rand_distr = "0.4"
+rand_pcg = "0.3"
+
+[profile.dev]
+opt-level = 1
+
+[profile.dev.package."*"]
+opt-level = 3
diff --git a/src/2d_shapes.rs b/src/2d_shapes.rs
new file mode 100644
index 0000000..7fa168f
--- /dev/null
+++ b/src/2d_shapes.rs
@@ -0,0 +1,55 @@
+//! Shows how to render simple primitive shapes with a single color.
+
+use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, setup)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+) {
+    commands.spawn(Camera2dBundle::default());
+
+    // Circle
+    commands.spawn(MaterialMesh2dBundle {
+        mesh: meshes.add(shape::Circle::new(50.).into()).into(),
+        material: materials.add(ColorMaterial::from(Color::PURPLE)),
+        transform: Transform::from_translation(Vec3::new(-150., 0., 0.)),
+        ..default()
+    });
+
+    // Rectangle
+    commands.spawn(SpriteBundle {
+        sprite: Sprite {
+            color: Color::rgb(0.25, 0.25, 0.75),
+            custom_size: Some(Vec2::new(50.0, 100.0)),
+            ..default()
+        },
+        transform: Transform::from_translation(Vec3::new(-50., 0., 0.)),
+        ..default()
+    });
+
+    // Quad
+    commands.spawn(MaterialMesh2dBundle {
+        mesh: meshes
+            .add(shape::Quad::new(Vec2::new(50., 100.)).into())
+            .into(),
+        material: materials.add(ColorMaterial::from(Color::LIME_GREEN)),
+        transform: Transform::from_translation(Vec3::new(50., 0., 0.)),
+        ..default()
+    });
+
+    // Hexagon
+    commands.spawn(MaterialMesh2dBundle {
+        mesh: meshes.add(shape::RegularPolygon::new(50., 6).into()).into(),
+        material: materials.add(ColorMaterial::from(Color::TURQUOISE)),
+        transform: Transform::from_translation(Vec3::new(150., 0., 0.)),
+        ..default()
+    });
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..3bcce63
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,36 @@
+pub mod timer;
+pub mod trips;
+use std::ops::{Add, AddAssign};
+
+use bevy::prelude::*;
+
+pub use timer::SimulationTimerPlugin;
+pub use trips::{Trip, TripPlugin, Trips};
+
+/// Coordinates x, y on the map.
+#[derive(Clone, Copy, Debug)]
+pub struct MapPosition(pub f32, pub f32);
+
+/// Unit used to represent time in a simulation, measured in number of [TIME_UNIT] after midnight.
+#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
+pub struct SimulationTime(pub usize);
+
+impl Add for SimulationTime {
+    type Output = SimulationTime;
+    fn add(self, rhs: SimulationTime) -> Self::Output {
+        Self(self.0 + rhs.0)
+    }
+}
+
+impl AddAssign for SimulationTime {
+    fn add_assign(&mut self, rhs: Self) {
+        self.0 += rhs.0;
+    }
+}
+
+#[derive(Component)]
+struct MainCamera;
+
+pub fn setup(mut commands: Commands) {
+    commands.spawn((Camera2dBundle::default(), MainCamera));
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..0bf1734
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,47 @@
+use bevy::prelude::*;
+use metroviz::*;
+use rand::Rng;
+use rand_distr::{Distribution, Normal, Uniform};
+use rand_pcg::Pcg64Mcg;
+
+fn random_color<R: Rng>(rng: &mut R) -> Color {
+    let uniform = Uniform::new(0.0, 1.0);
+    let r = uniform.sample(rng);
+    let g = uniform.sample(rng);
+    let b = uniform.sample(rng);
+    Color::rgb(r, g, b)
+}
+
+fn main() {
+    let n = 10;
+    let j = 16;
+    let mut trips = Vec::with_capacity(n);
+    let mut rng = Pcg64Mcg::new(2031996);
+    let uniform = Uniform::new(-500.0, 500.0);
+    let normal = Normal::new(0.0, 3.0).unwrap();
+    for _ in 0..n {
+        let mut x = uniform.sample(&mut rng);
+        let mut y = uniform.sample(&mut rng);
+        let mut path = Vec::with_capacity(j);
+        for _ in 0..j {
+            x = x + normal.sample(&mut rng);
+            y = y + normal.sample(&mut rng);
+            path.push(MapPosition(x, y));
+        }
+        let trip = Trip {
+            start_time: SimulationTime(5),
+            end_time: SimulationTime(5 + j - 1),
+            path,
+            width: 0.3,
+            length: 0.6,
+            color: random_color(&mut rng),
+        };
+        trips.push(trip);
+    }
+
+    App::new()
+        .insert_resource(Trips(trips))
+        .add_plugins((DefaultPlugins, SimulationTimerPlugin, TripPlugin))
+        .add_systems(Startup, setup)
+        .run();
+}
diff --git a/src/timer.rs b/src/timer.rs
new file mode 100644
index 0000000..69b9b6e
--- /dev/null
+++ b/src/timer.rs
@@ -0,0 +1,95 @@
+use crate::SimulationTime;
+use bevy::prelude::*;
+
+/// Current simulation time (in [TIME_UNIT] after midnight).
+#[derive(Resource)]
+pub struct SimulationTimer {
+    time: SimulationTime,
+    timer: Timer,
+}
+
+impl SimulationTimer {
+    /// Returns `true` if the current simulation time is within the given start and end times.
+    pub fn covers(&self, start: SimulationTime, end: SimulationTime) -> bool {
+        self.time >= start && self.time <= end
+    }
+}
+
+/// Event that triggers when the [SimulationTimer] is updated.
+#[derive(Default, Event)]
+pub struct SimulationTimerUpdated(pub SimulationTime);
+
+pub struct SimulationTimerPlugin;
+
+impl Plugin for SimulationTimerPlugin {
+    fn build(&self, app: &mut App) {
+        app.insert_resource(SimulationTimer {
+            time: SimulationTime(0),
+            timer: Timer::from_seconds(1.0, TimerMode::Repeating),
+        })
+        .add_event::<SimulationTimerUpdated>()
+        .add_systems(Startup, initialize_ui)
+        .add_systems(Update, (update_simulation_timer, debug_simulation_timer));
+    }
+}
+
+fn initialize_ui(mut commands: Commands, asset_server: Res<AssetServer>) {
+    commands
+        .spawn(NodeBundle {
+            style: Style {
+                width: Val::Percent(100.0),
+                height: Val::Px(100.0),
+                position_type: PositionType::Absolute,
+                bottom: Val::Px(0.0),
+                align_items: AlignItems::Center,
+                justify_content: JustifyContent::Center,
+                ..default()
+            },
+            background_color: BackgroundColor(Color::WHITE),
+            ..default()
+        })
+        .with_children(|parent| {
+            parent
+                .spawn(ButtonBundle {
+                    style: Style {
+                        width: Val::Px(30.0),
+                        height: Val::Px(30.0),
+                        border: UiRect::all(Val::Px(2.0)),
+                        justify_content: JustifyContent::Center,
+                        align_items: AlignItems::Center,
+                        ..default()
+                    },
+                    border_color: BorderColor(Color::BLACK),
+                    background_color: BackgroundColor(Color::GRAY),
+                    ..default()
+                })
+                .with_children(|parent| {
+                    parent.spawn(TextBundle::from_section(
+                        "\u{23f5}",
+                        TextStyle {
+                            font: asset_server.load("fonts/Symbola.ttf"),
+                            font_size: 40.0,
+                            color: Color::WHITE,
+                        },
+                    ));
+                });
+        });
+}
+
+fn update_simulation_timer(
+    time: Res<Time>,
+    mut simulation_timer: ResMut<SimulationTimer>,
+    mut event_writer: EventWriter<SimulationTimerUpdated>,
+) {
+    simulation_timer.timer.tick(time.delta());
+    if simulation_timer.timer.just_finished() {
+        simulation_timer.time += SimulationTime(1);
+        event_writer.send(SimulationTimerUpdated(simulation_timer.time))
+    }
+}
+
+fn debug_simulation_timer(mut timer_events: EventReader<SimulationTimerUpdated>) {
+    for ev in timer_events.iter() {
+        println!("{:?}", ev.0);
+    }
+}
diff --git a/src/trips.rs b/src/trips.rs
new file mode 100644
index 0000000..b749914
--- /dev/null
+++ b/src/trips.rs
@@ -0,0 +1,136 @@
+use bevy::prelude::{shape::Quad, *};
+
+use crate::timer::SimulationTimerUpdated;
+use crate::{MapPosition, SimulationTime};
+use std::ops::{Deref, Index};
+
+/// Simulation time at which the entity starts appearing.
+#[derive(Clone, Copy, Debug, Component)]
+struct StartTime(SimulationTime);
+
+/// Simulation time at which the entity disappears.
+#[derive(Clone, Copy, Debug, Component)]
+struct EndTime(SimulationTime);
+
+/// Index of the trip in the [Trips] resource.
+#[derive(Clone, Copy, Debug, Component)]
+struct TripIndex(usize);
+
+/// Path followed by an entity.
+///
+/// The path is represented by the sequence of [MapPosition] traveled by the entity (one for each
+/// [TIME_UNIT]). The number of [MapPosition] should be equal to the time duration of the path in
+/// [TIME_UNIT].
+#[derive(Component)]
+struct Path(&'static [MapPosition]);
+
+/// A vehicle or agent moving on the map.
+#[derive(Bundle)]
+struct TripBundle {
+    trip_id: TripIndex,
+    start_time: StartTime,
+    end_time: EndTime,
+    mesh: ColorMesh2dBundle,
+}
+
+pub struct Trip {
+    pub start_time: SimulationTime,
+    pub end_time: SimulationTime,
+    pub path: Vec<MapPosition>,
+    pub width: f32,
+    pub length: f32,
+    pub color: Color,
+}
+
+impl Trip {
+    fn get_coords_at_time(&self, time: SimulationTime) -> Vec3 {
+        debug_assert!(
+            time >= self.start_time,
+            "{:?} < {:?}",
+            time,
+            self.start_time
+        );
+        debug_assert!(time <= self.end_time, "{:?} > {:?}", time, self.end_time);
+        let idx = time.0 - self.start_time.0;
+        let pos = self.path[idx];
+        Vec3::new(pos.0, pos.1, 0.0)
+    }
+}
+
+#[derive(Resource)]
+pub struct Trips(pub Vec<Trip>);
+
+impl Deref for Trips {
+    type Target = Vec<Trip>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Index<TripIndex> for Trips {
+    type Output = Trip;
+    fn index(&self, index: TripIndex) -> &Self::Output {
+        &self.0[index.0]
+    }
+}
+
+/// Plugin to manage the trips.
+pub struct TripPlugin;
+
+impl Plugin for TripPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(Startup, spawn_trips)
+            .add_systems(Update, toggle_trips_visibility);
+    }
+}
+
+fn spawn_trips(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+    trips: Res<Trips>,
+) {
+    for (index, trip) in trips.iter().enumerate() {
+        commands.spawn(TripBundle {
+            trip_id: TripIndex(index),
+            start_time: StartTime(trip.start_time),
+            end_time: EndTime(trip.end_time),
+            mesh: ColorMesh2dBundle {
+                mesh: meshes
+                    .add(Quad::new(Vec2::new(trip.width, trip.length)).into())
+                    .into(),
+                material: materials.add(ColorMaterial::from(trip.color)),
+                visibility: Visibility::Hidden,
+                ..default()
+            },
+        });
+    }
+}
+
+/// Shows / hides trips according to the current simulation time and the start / end time of the
+/// trips.
+fn toggle_trips_visibility(
+    mut events: EventReader<SimulationTimerUpdated>,
+    trips: Res<Trips>,
+    mut query: Query<(
+        &TripIndex,
+        &StartTime,
+        &EndTime,
+        &mut Visibility,
+        &mut Transform,
+    )>,
+) {
+    if let Some(event) = events.iter().last() {
+        println!("hello world!");
+        let current_time = event.0;
+        for (&trip_id, start_time, end_time, mut vis, mut transform) in query.iter_mut() {
+            if current_time >= start_time.0 && current_time <= end_time.0 {
+                *vis = Visibility::Visible;
+                let trip = &trips[trip_id];
+                transform.translation = trip.get_coords_at_time(current_time);
+            } else {
+                *vis = Visibility::Hidden;
+            }
+        }
+    }
+}