An air carrier pilot reported they were given taxi clearance via taxiways a; P1; U to runway 28; but...

Narrative:

While cleared to taxi out by ATC for departure on runway 28; we took a wrong turn to enter taxiway U. Bwi ground cleared us to taxi via taxiways a; P1; and U. Instead we joined U from P taxiing via a; east; P; and U. Departing from the X gate alleyway at night; contributing factors included an absence of taxiway signage; multiple illuminated construction barriers; and an aircraft on taxiway P. When questioned by ground about the incorrect turn; we acknowledged the mistake and no further discussion occurred. The remainder of the flight was conducted uneventfully. Taxiway signage could be improved coming out the alleyway of the X gates. Aircrews should not taxi their aircraft until ATC routing instructions are mutually understood and verified.

Original NASA ASRS Text

Title: An air carrier pilot reported they were given taxi clearance via Taxiways A; P1; U to Runway 28; but because of night conditions; construction barrier lights and poor signage transitioned to U at P. ATC alerted about the error.

Narrative: While cleared to taxi out by ATC for departure on Runway 28; we took a wrong turn to enter Taxiway U. BWI Ground cleared us to taxi via Taxiways A; P1; and U. Instead we joined U from P taxiing via A; E; P; and U. Departing from the X Gate alleyway at night; contributing factors included an absence of taxiway signage; multiple illuminated construction barriers; and an aircraft on Taxiway P. When questioned by Ground about the incorrect turn; we acknowledged the mistake and no further discussion occurred. The remainder of the flight was conducted uneventfully. Taxiway signage could be improved coming out the alleyway of the X gates. Aircrews should not taxi their aircraft until ATC routing instructions are mutually understood and verified.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1203087
Time
Date	201409
Local Time Of Day	1801-2400
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Experience	Flight Crew Last 90 Days 200 Flight Crew Type 8100
Events
Anomaly	Deviation - Procedural Clearance Ground Incursion Taxiway

An air carrier pilot reported they were given taxi clearance via taxiways a; P1; U to runway 28; but because of night conditions; construction barrier lights and poor signage transitioned to U at P. ATC alerted about the error.