diff --git a/rmf_traffic/include/rmf_traffic/schedule/Database.hpp b/rmf_traffic/include/rmf_traffic/schedule/Database.hpp
index 6318012f..2d27b4b1 100644
--- a/rmf_traffic/include/rmf_traffic/schedule/Database.hpp
+++ b/rmf_traffic/include/rmf_traffic/schedule/Database.hpp
@@ -113,7 +113,7 @@ class Database : public ItineraryViewer, public Writer, public Snappable
 
   // Documentation inherited from Viewer
   std::shared_ptr<const ParticipantDescription> get_participant(
-    std::size_t participant_id) const final;
+    ParticipantId participant_id) const final;
 
   // Documentation inherited from Viewer
   Version latest_version() const;
@@ -125,11 +125,11 @@ class Database : public ItineraryViewer, public Writer, public Snappable
 
   // Documentation inherited from ItineraryViewer
   std::optional<ItineraryView> get_itinerary(
-    std::size_t participant_id) const final;
+    ParticipantId participant_id) const final;
 
   // Documentation inherited from ItineraryViewer
   std::optional<PlanId> get_current_plan_id(
-    std::size_t participant_id) const final;
+    ParticipantId participant_id) const final;
 
   // Documentation inherited from ItineraryViewer
   const std::vector<CheckpointId>* get_current_progress(
diff --git a/rmf_traffic/include/rmf_traffic/schedule/Mirror.hpp b/rmf_traffic/include/rmf_traffic/schedule/Mirror.hpp
index 14c3c9e5..f6a6108d 100644
--- a/rmf_traffic/include/rmf_traffic/schedule/Mirror.hpp
+++ b/rmf_traffic/include/rmf_traffic/schedule/Mirror.hpp
@@ -51,11 +51,11 @@ class Mirror : public ItineraryViewer, public Snappable
 
   // Documentation inherited from Viewer
   std::shared_ptr<const ParticipantDescription> get_participant(
-    std::size_t participant_id) const final;
+    ParticipantId participant_id) const final;
 
   // Documentation inherited from Viewer
   std::optional<ItineraryView> get_itinerary(
-    std::size_t participant_id) const final;
+    ParticipantId participant_id) const final;
 
   // Documentation inherited from Viewer
   std::optional<Version> latest_version() const;
diff --git a/rmf_traffic/src/rmf_traffic/schedule/Database.cpp b/rmf_traffic/src/rmf_traffic/schedule/Database.cpp
index 3f6dd48c..2377692e 100644
--- a/rmf_traffic/src/rmf_traffic/schedule/Database.cpp
+++ b/rmf_traffic/src/rmf_traffic/schedule/Database.cpp
@@ -1303,7 +1303,7 @@ const std::unordered_set<ParticipantId>& Database::participant_ids() const
 
 //==============================================================================
 std::shared_ptr<const ParticipantDescription> Database::get_participant(
-  std::size_t participant_id) const
+  ParticipantId participant_id) const
 {
   const auto state_it = _pimpl->descriptions.find(participant_id);
   if (state_it == _pimpl->descriptions.end())
@@ -1320,7 +1320,7 @@ Version Database::latest_version() const
 
 //==============================================================================
 std::optional<ItineraryView> Database::get_itinerary(
-  const std::size_t participant_id) const
+  const ParticipantId participant_id) const
 {
   const auto state_it = _pimpl->states.find(participant_id);
   if (state_it == _pimpl->states.end())
@@ -1345,7 +1345,7 @@ std::optional<ItineraryView> Database::get_itinerary(
 
 //==============================================================================
 std::optional<PlanId> Database::get_current_plan_id(
-  const std::size_t participant_id) const
+  const ParticipantId participant_id) const
 {
   const auto state_it = _pimpl->states.find(participant_id);
   if (state_it == _pimpl->states.end())
diff --git a/rmf_traffic/src/rmf_traffic/schedule/Mirror.cpp b/rmf_traffic/src/rmf_traffic/schedule/Mirror.cpp
index 4c1d7105..e84006a0 100644
--- a/rmf_traffic/src/rmf_traffic/schedule/Mirror.cpp
+++ b/rmf_traffic/src/rmf_traffic/schedule/Mirror.cpp
@@ -255,7 +255,7 @@ const std::unordered_set<ParticipantId>& Mirror::participant_ids() const
 
 //==============================================================================
 std::shared_ptr<const ParticipantDescription> Mirror::get_participant(
-  std::size_t participant_id) const
+  ParticipantId participant_id) const
 {
   const auto p = _pimpl->descriptions.find(participant_id);
   if (p == _pimpl->descriptions.end())
@@ -272,7 +272,7 @@ std::optional<Version> Mirror::latest_version() const
 
 //==============================================================================
 std::optional<ItineraryView> Mirror::get_itinerary(
-  const std::size_t participant_id) const
+  const ParticipantId participant_id) const
 {
   const auto p = _pimpl->states.find(participant_id);
   if (p == _pimpl->states.end())
@@ -297,7 +297,7 @@ std::optional<ItineraryView> Mirror::get_itinerary(
 
 //==============================================================================
 std::optional<PlanId> Mirror::get_current_plan_id(
-  const std::size_t participant_id) const
+  const ParticipantId participant_id) const
 {
   const auto p = _pimpl->states.find(participant_id);
   if (p == _pimpl->states.end())
diff --git a/rmf_traffic/test/unit/schedule/test_Spacetime.cpp b/rmf_traffic/test/unit/schedule/test_Spacetime.cpp
index e96cfb62..140ac524 100644
--- a/rmf_traffic/test/unit/schedule/test_Spacetime.cpp
+++ b/rmf_traffic/test/unit/schedule/test_Spacetime.cpp
@@ -41,8 +41,8 @@ SCENARIO("Testing intersection of spacetime with trajectories")
   const auto region_box_shape = rmf_traffic::geometry::make_final_convex<
     rmf_traffic::geometry::Box>(10.0, 1.0);
 
-  std::chrono::_V2::steady_clock::time_point lower_time_bound = time;
-  std::chrono::_V2::steady_clock::time_point upper_time_bound = time+10s;
+  std::chrono::steady_clock::time_point lower_time_bound = time;
+  std::chrono::steady_clock::time_point upper_time_bound = time+10s;
 
   rmf_traffic::internal::Spacetime region = {
     &lower_time_bound,
@@ -117,8 +117,8 @@ SCENARIO("Testing intersction of various spacetimes and trajectories")
   using namespace std::chrono_literals;
   auto time = std::chrono::steady_clock::now();
   Eigen::Isometry2d tf = Eigen::Isometry2d::Identity();
-  std::chrono::_V2::steady_clock::time_point lower_time_bound;
-  std::chrono::_V2::steady_clock::time_point upper_time_bound;
+  std::chrono::steady_clock::time_point lower_time_bound;
+  std::chrono::steady_clock::time_point upper_time_bound;
 
   const auto region_box_shape = rmf_traffic::geometry::make_final_convex<
     rmf_traffic::geometry::Box>(10.0, 1.0);
@@ -1210,8 +1210,8 @@ SCENARIO("Testing intersection of curved trajectory with various spacetimes")
   GIVEN("spacetime that encompasses the trajectory in space and time")
   {
     //creating space to create spacetime
-    std::chrono::_V2::steady_clock::time_point lower_time_bound = time;
-    std::chrono::_V2::steady_clock::time_point upper_time_bound = time+10s;
+    std::chrono::steady_clock::time_point lower_time_bound = time;
+    std::chrono::steady_clock::time_point upper_time_bound = time+10s;
     Eigen::Isometry2d tf = Eigen::Isometry2d::Identity();
 
     rmf_traffic::internal::Spacetime region = {
@@ -1227,8 +1227,8 @@ SCENARIO("Testing intersection of curved trajectory with various spacetimes")
   GIVEN("spacetime that encompasses the trajectory in space but not time")
   {
     //creating space to create spacetime
-    std::chrono::_V2::steady_clock::time_point lower_time_bound = time+20s;
-    std::chrono::_V2::steady_clock::time_point upper_time_bound = time+30s;
+    std::chrono::steady_clock::time_point lower_time_bound = time+20s;
+    std::chrono::steady_clock::time_point upper_time_bound = time+30s;
     Eigen::Isometry2d tf = Eigen::Isometry2d::Identity();
 
     rmf_traffic::internal::Spacetime region = {
@@ -1244,8 +1244,8 @@ SCENARIO("Testing intersection of curved trajectory with various spacetimes")
   GIVEN("spacetime that partially intersects the trajectory in space and time")
   {
     //creating space to create spacetime
-    std::chrono::_V2::steady_clock::time_point lower_time_bound = time;
-    std::chrono::_V2::steady_clock::time_point upper_time_bound = time+10s;
+    std::chrono::steady_clock::time_point lower_time_bound = time;
+    std::chrono::steady_clock::time_point upper_time_bound = time+10s;
     Eigen::Isometry2d tf = Eigen::Isometry2d::Identity();
 
     rmf_traffic::internal::Spacetime region = {
@@ -1263,8 +1263,8 @@ SCENARIO("Testing intersection of curved trajectory with various spacetimes")
 SCENARIO("Testing multi-waypoint trajectories with various spacetimes")
 {
   using namespace std::chrono_literals;
-  std::chrono::_V2::steady_clock::time_point lower_time_bound;
-  std::chrono::_V2::steady_clock::time_point upper_time_bound;
+  std::chrono::steady_clock::time_point lower_time_bound;
+  std::chrono::steady_clock::time_point upper_time_bound;
 
   const auto small_circle_shape = rmf_traffic::geometry::make_final_convex<
     rmf_traffic::geometry::Circle>(0.5);