diff --git a/src/InfrastructureOptimizationModels.jl b/src/InfrastructureOptimizationModels.jl
index 6fa5498..e62ba70 100644
--- a/src/InfrastructureOptimizationModels.jl
+++ b/src/InfrastructureOptimizationModels.jl
@@ -468,6 +468,9 @@ export ReservationVariable
 export PiecewiseLinearCostVariable
 export RateofChangeConstraintSlackUp, RateofChangeConstraintSlackDown
 export DCVoltage
+# Flow-direction trait for variable types
+export FlowSign, FlowInjection, FlowWithdrawal, FlowUndirected
+export flow_sign, multiplier_from_sign
 # Abstract types needed by POM for type hierarchy
 export SparseVariableType, InterpolationVariableType, BinaryInterpolationVariableType
 
diff --git a/src/common_models/rateofchange_constraints.jl b/src/common_models/rateofchange_constraints.jl
index 3785d6d..4aaae74 100644
--- a/src/common_models/rateofchange_constraints.jl
+++ b/src/common_models/rateofchange_constraints.jl
@@ -1,4 +1,3 @@
-# NOTE: not included currently.
 function _get_minutes_per_period(container::OptimizationContainer)
     resolution = get_resolution(container)
     if resolution > Dates.Minute(1)
diff --git a/src/core/standard_variables_expressions.jl b/src/core/standard_variables_expressions.jl
index 58cf876..6522e19 100644
--- a/src/core/standard_variables_expressions.jl
+++ b/src/core/standard_variables_expressions.jl
@@ -36,6 +36,38 @@ struct RateofChangeConstraintSlackDown <: VariableType end
 # HVDC Variables (used in add_pwl_methods)
 struct DCVoltage <: VariableType end
 
+#################################################################################
+# Flow direction trait
+#
+# Encodes the sign with which a variable contributes to a power-balance
+# expression. Replaces scattered `get_variable_multiplier(...) = ±1.0` overrides
+# whose only signal is the variable type itself. Device-driven sign overrides
+# (e.g. anything on `PSY.ElectricLoad`) still live in POM as more-specific
+# dispatches.
+#################################################################################
+
+# Holy-traits style: `flow_sign` returns a *type*, and `multiplier_from_sign`
+# dispatches on `::Type{<:FlowSign}`. Both layers resolve at compile time so the
+# numeric multiplier folds away at every call site.
+abstract type FlowSign end
+struct FlowInjection <: FlowSign end
+struct FlowWithdrawal <: FlowSign end
+struct FlowUndirected <: FlowSign end
+
+# Default: no directional meaning attached to the variable type.
+flow_sign(::Type{<:VariableType}) = FlowUndirected
+
+multiplier_from_sign(::Type{FlowInjection}) = 1.0
+multiplier_from_sign(::Type{FlowWithdrawal}) = -1.0
+# Variables without flow semantics (OnVariable, StartVariable, ...) keep the
+# legacy 1.0 default so callers that don't care about sign still work.
+multiplier_from_sign(::Type{FlowUndirected}) = 1.0
+
+# Standard variable types defined here:
+flow_sign(::Type{ActivePowerVariable}) = FlowInjection
+flow_sign(::Type{ActivePowerInVariable}) = FlowWithdrawal
+flow_sign(::Type{ActivePowerOutVariable}) = FlowInjection
+
 #################################################################################
 # Standard Expression Types
 # These are the base expression types for aggregating terms
diff --git a/test/InfrastructureOptimizationModelsTests.jl b/test/InfrastructureOptimizationModelsTests.jl
index f218b68..81adc61 100644
--- a/test/InfrastructureOptimizationModelsTests.jl
+++ b/test/InfrastructureOptimizationModelsTests.jl
@@ -114,6 +114,7 @@ function run_tests()
                     # TODO service_model.jl
                     include(joinpath(TEST_DIR, "test_settings.jl"))
                     # standard_variables_expressions.jl: low complexity
+                    include(joinpath(TEST_DIR, "test_flow_sign.jl"))
                     # time_series_parameter_types.jl: low complexity
 
                     # --- objective_function/ subfolder ---
diff --git a/test/Project.toml b/test/Project.toml
index fed99d0..0ec6c3d 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -9,7 +9,6 @@ DataFramesMeta = "1313f7d8-7da2-5740-9ea0-a2ca25f37964"
 DataStructures = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 HiGHS = "87dc4568-4c63-4d18-b0c0-bb2238e4078b"
-InfrastructureOptimizationModels = "bed98974-b02a-5e2f-9ee0-a103f5c45069"
 InfrastructureSystems = "2cd47ed4-ca9b-11e9-27f2-ab636a7671f1"
 Ipopt = "b6b21f68-93f8-5de0-b562-5493be1d77c9"
 JSON3 = "0f8b85d8-7281-11e9-16c2-39a750bddbf1"
@@ -30,7 +29,6 @@ UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 UnoSolver = "1baa60ac-02f7-4b39-a7a8-2f4f58486b05"
 
 [sources]
-InfrastructureOptimizationModels = {path = ".."}
 InfrastructureSystems = {rev = "IS4", url = "https://github.com/Sienna-Platform/InfrastructureSystems.jl"}
 
 [compat]
diff --git a/test/test_flow_sign.jl b/test/test_flow_sign.jl
new file mode 100644
index 0000000..65947fb
--- /dev/null
+++ b/test/test_flow_sign.jl
@@ -0,0 +1,28 @@
+@testset "FlowSign trait" begin
+    @testset "multiplier_from_sign maps to expected ±1.0" begin
+        @test IOM.multiplier_from_sign(IOM.FlowInjection) == 1.0
+        @test IOM.multiplier_from_sign(IOM.FlowWithdrawal) == -1.0
+        @test IOM.multiplier_from_sign(IOM.FlowUndirected) == 1.0
+    end
+
+    @testset "flow_sign defaults to FlowUndirected" begin
+        # Any VariableType without an explicit override falls back to FlowUndirected.
+        # OnVariable / StartVariable / etc. have no flow semantics by design.
+        @test IOM.flow_sign(OnVariable) === IOM.FlowUndirected
+        @test IOM.flow_sign(StartVariable) === IOM.FlowUndirected
+        @test IOM.flow_sign(StopVariable) === IOM.FlowUndirected
+    end
+
+    @testset "Standard active-power variables carry the correct sign" begin
+        @test IOM.flow_sign(ActivePowerVariable) === IOM.FlowInjection
+        @test IOM.flow_sign(ActivePowerInVariable) === IOM.FlowWithdrawal
+        @test IOM.flow_sign(ActivePowerOutVariable) === IOM.FlowInjection
+    end
+
+    @testset "Roundtrip: multiplier_from_sign ∘ flow_sign" begin
+        @test IOM.multiplier_from_sign(IOM.flow_sign(ActivePowerVariable)) == 1.0
+        @test IOM.multiplier_from_sign(IOM.flow_sign(ActivePowerInVariable)) == -1.0
+        @test IOM.multiplier_from_sign(IOM.flow_sign(ActivePowerOutVariable)) == 1.0
+        @test IOM.multiplier_from_sign(IOM.flow_sign(OnVariable)) == 1.0
+    end
+end