diff --git a/tm2py/components/network/highway/highway_assign.py b/tm2py/components/network/highway/highway_assign.py
index 16fe772f..3401e6e2 100644
--- a/tm2py/components/network/highway/highway_assign.py
+++ b/tm2py/components/network/highway/highway_assign.py
@@ -298,6 +298,12 @@ def _get_assignment_spec(
 
         """
         relative_gap = self.config.relative_gap
+        # if relative is a list, get the corresponding value for the current iteration
+        if relative_gap and isinstance(relative_gap, list):
+            if self.controller.iteration == 0:
+                relative_gap = relative_gap[0]
+            else:
+                relative_gap = relative_gap[self.controller.iteration - 1]
         max_iterations = self.config.max_iterations
         # NOTE: mazmazvol as background traffic in link.data1 ("ul1")
         base_spec = {
diff --git a/tm2py/config.py b/tm2py/config.py
index 72ab3387..6ee03588 100644
--- a/tm2py/config.py
+++ b/tm2py/config.py
@@ -911,7 +911,8 @@ class HighwayConfig(ConfigItem):
     Properties:
         generic_highway_mode_code: single character unique mode ID for entire
             highway network (no excluded_links)
-        relative_gap: target relative gap stopping criteria
+        relative_gap: target relative gap stopping criteria. specify a single value float
+            for all global iterations or a list with values for each global iteration.
         max_iterations: maximum iterations stopping criteria
         area_type_buffer_dist_miles: used to in calculation to categorize link @areatype
             The area type is determined based on the average density of nearby
@@ -929,10 +930,12 @@ class HighwayConfig(ConfigItem):
             see HighwayClassConfig
         capclass_lookup: index cross-reference table from the link @capclass value
             to the free-flow speed, capacity, and critical speed values
+        interchange_nodes_file: relative path to the interchange nodes file, this is
+            used for calculating highway reliability
     """
 
     generic_highway_mode_code: str = Field(min_length=1, max_length=1)
-    relative_gap: float = Field(ge=0)
+    relative_gap: float | Tuple[float, ...] = Field(ge=0)
     max_iterations: int = Field(ge=0)
     area_type_buffer_dist_miles: float = Field(gt=0)
     drive_access_output_skim_path: Optional[str] = Field(default=None)
@@ -1334,6 +1337,18 @@ def maz_skim_period_exists(cls, value, values):
             ), "maz_to_maz -> skim_period -> name not found in time_periods list"
         return value
 
+    @validator("highway_relative_gap")
+    def relative_gap_length(cls, value, values):
+        """Validate highway.relative_gap is a list of the same length as global iterations."""
+        if "end_iteration" in values:
+            if isinstance(value, float):
+                return value
+            assert (
+                len(value) == len(values["end_iteration"]),
+                "relative_gap must be the same length as end_iteration",
+            )
+        return value
+
 
 def _load_toml(path: str) -> dict:
     """Load config from toml file at path."""