Multicolumn aligns text always right

Question

I'm in the Latex tabular environment. I want to align the text in a multicolumn to the left, but it does not work. It is always alignt to the right.

Here is my code:

\begin{tabular}{|p{2cm}|p{2cm}|p{2cm}|p{2cm}|p{2cm}|}\hline
\textbf{number of lanes:} & \multicolumn{2}{l|}\textbf{8 (20 m width)} & \multicolumn{2}{l|} \textbf{10 (25 m width)}\\
  & distance & free space loss & distance & free space loss \\\hline 
\textbf{lane length 25 m} & 16.008 m & 10 dB & 17.678 m & 30 dB\\\hline
\textbf{lane length 50 m} & 26.926 m & 20 dB & 27.951 m & 40 dB\\\hline
\end{tabular}

and the output is always:

Waht I'm doing wrong?

I'm on Kubuntu 20.10 with Kile kile 2.9.93

OS: Kubuntu 20.10 KDE-Plasma-Version: 5.19.5 KDE-Frameworks-Version: 5.74.0 Qt-Version: 5.14.2 Kernel-Version: 5.8.0-63-generic Architecture: 64-bit Prozessors: 4 × Intel® Core™ i5-3320M CPU @ 2.60GHz RAM: 7,6 GiB GPU: Mesa DRI Intel® HD Graphics 4000

(If you ask, it's for a vital parameters telemetry radio system for swimmers)

Answer 1

You may give a chance to tabularray and siunitx (loaded as tabularray library) packages. Using them you will get simple control on cells contents aligning and writing units. For details of all possibilities of those two powerful packages are thoroughly described in theirs documentation.

• a case, when all cells contents is left aligned:

\documentclass{article}
\usepackage{tabularray}
\UseTblrLibrary{siunitx}

\begin{document}
    \begin{table}[ht]
    \centering
    \sisetup{text-series-to-math}
\begin{tblr}{hline{1,3-Z}, vlines,
             colspec = {*{5}{X[l,m]}}, 
             column{1} = {font=\bfseries},
             row{1} = {font=\bfseries}
             }
number of lanes:
    &   \SetCell[c=2]{l} 8 (\qty{20}{m} width)
        &   &   \SetCell[c=2]{l} 10 (\qty{25}{m} width)    
                &                       \\
    &   distance 
        &   free space loss 
            &   distance 
                &   free space loss     \\
lane length \qty[unit-font-command=\mathbf]{25}{m} 
    & \qty{16.008}{m} 
        &   \qty{10}{dB} 
            &   \qty{17.678}{m} 
                &   \qty{30}{dB}        \\
lane length \qty[unit-font-command=\mathbf]{50}{m} 
    &   \qty{26.926}{m} 
        &   \qty{20}{dB} 
            &   \qty{27.951}{m} 
                &   \qty{40}{dB}        \\
\end{tblr}
    \end{table}
\end{document}

• a case, where except first one a cells contents are centered. In this case the table specification in above MWE is changed to:

\begin{tblr}{hline{1,3-Z}, vlines,
             colspec = {X[l,m]*{4}{X[c,m]}},    % <---
             column{1} = {font=\bfseries},
             row{1} = {font=\bfseries}
             }

and multi column cells specification to:

\SetCell[c=2]{c}

which gives:

Edit:

• one more possible table layout:

which you can get with the following table preamble:

\begin{tblr}{hlines, vlines,
             colspec = {X[l,m]*{4}{X[c,m]}},    
             column{1} = {font=\bfseries},
             row{1} = {font=\bfseries}
             }

Answer 2

You forgot braces {} around the text of the \multicolumn. I also added \raggedright to get a nicer layout. I did this by defining a new column type q.

\documentclass{article}
\usepackage{array}
\newcolumntype{q}[1]{>{\raggedright\arraybackslash}p{#1}}
\begin{document}
\begin{tabular}{|q{2cm}|q{2cm}|q{2cm}|q{2cm}|q{2cm}|}\hline
\textbf{number of lanes:} & \multicolumn{2}{l|}{\textbf{8 (20 m width)}} & \multicolumn{2}{l|} {\textbf{10 (25 m width)}}\\
  & distance & free space loss & distance & free space loss \\\hline 
\textbf{lane length 25 m} & 16.008 m & 10 dB & 17.678 m & 30 dB\\\hline
\textbf{lane length 50 m} & 26.926 m & 20 dB & 27.951 m & 40 dB\\\hline
\end{tabular}
\end{document}